Calculus Examples

$x^{2} e^{- x}$

Step 1

Find the first derivative.

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Step 1.1

Differentiate using the Product Rule which states that $\frac{d}{d x} [f (x) g (x)]$ is $f (x) \frac{d}{d x} [g (x)] + g (x) \frac{d}{d x} [f (x)]$ where $f (x) = x^{2}$ and $g (x) = e^{- x}$ .

$x^{2} \frac{d}{d x} [e^{- x}] + e^{- x} \frac{d}{d x} [x^{2}]$

Step 1.2

Differentiate using the chain rule, which states that $\frac{d}{d x} [f (g (x))]$ is $f' (g (x)) g' (x)$ where $f (x) = e^{x}$ and $g (x) = - x$ .

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Step 1.2.1

To apply the Chain Rule, set $u$ as $- x$ .

$x^{2} (\frac{d}{d u} [e^{u}] \frac{d}{d x} [- x]) + e^{- x} \frac{d}{d x} [x^{2}]$

Step 1.2.2

Differentiate using the Exponential Rule which states that $\frac{d}{d u} [a^{u}]$ is $a^{u} \ln (a)$ where $a$ = $e$ .

$x^{2} (e^{u} \frac{d}{d x} [- x]) + e^{- x} \frac{d}{d x} [x^{2}]$

Step 1.2.3

Replace all occurrences of $u$ with $- x$ .

$x^{2} (e^{- x} \frac{d}{d x} [- x]) + e^{- x} \frac{d}{d x} [x^{2}]$

Step 1.3

Differentiate.

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Step 1.3.1

Since $- 1$ is constant with respect to $x$ , the derivative of $- x$ with respect to $x$ is $- \frac{d}{d x} [x]$ .

$x^{2} (e^{- x} (- \frac{d}{d x} [x])) + e^{- x} \frac{d}{d x} [x^{2}]$

Step 1.3.2

Differentiate using the Power Rule which states that $\frac{d}{d x} [x^{n}]$ is $n x^{n - 1}$ where $n = 1$ .

$x^{2} (e^{- x} (- 1 \cdot 1)) + e^{- x} \frac{d}{d x} [x^{2}]$

Step 1.3.3

Simplify the expression.

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Step 1.3.3.1

Multiply $- 1$ by $1$ .

$x^{2} (e^{- x} \cdot - 1) + e^{- x} \frac{d}{d x} [x^{2}]$

Step 1.3.3.2

Move $- 1$ to the left of $e^{- x}$ .

$x^{2} (- 1 \cdot e^{- x}) + e^{- x} \frac{d}{d x} [x^{2}]$

Step 1.3.3.3

Rewrite $- 1 e^{- x}$ as $- e^{- x}$ .

$x^{2} (- e^{- x}) + e^{- x} \frac{d}{d x} [x^{2}]$

Step 1.3.4

Differentiate using the Power Rule which states that $\frac{d}{d x} [x^{n}]$ is $n x^{n - 1}$ where $n = 2$ .

$x^{2} (- e^{- x}) + e^{- x} (2 x)$

Step 1.4

Simplify.

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Step 1.4.1

Reorder terms.

$- e^{- x} x^{2} + 2 e^{- x} x$

Step 1.4.2

Reorder factors in $- e^{- x} x^{2} + 2 e^{- x} x$ .

$f' (x) = - x^{2} e^{- x} + 2 x e^{- x}$

Step 2

Find the second derivative.

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Step 2.1

By the Sum Rule, the derivative of $- x^{2} e^{- x} + 2 x e^{- x}$ with respect to $x$ is $\frac{d}{d x} [- x^{2} e^{- x}] + \frac{d}{d x} [2 x e^{- x}]$ .

$\frac{d}{d x} [- x^{2} e^{- x}] + \frac{d}{d x} [2 x e^{- x}]$

Step 2.2

Evaluate $\frac{d}{d x} [- x^{2} e^{- x}]$ .

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Step 2.2.1

Since $- 1$ is constant with respect to $x$ , the derivative of $- x^{2} e^{- x}$ with respect to $x$ is $- \frac{d}{d x} [x^{2} e^{- x}]$ .

$- \frac{d}{d x} [x^{2} e^{- x}] + \frac{d}{d x} [2 x e^{- x}]$

Step 2.2.2

Differentiate using the Product Rule which states that $\frac{d}{d x} [f (x) g (x)]$ is $f (x) \frac{d}{d x} [g (x)] + g (x) \frac{d}{d x} [f (x)]$ where $f (x) = x^{2}$ and $g (x) = e^{- x}$ .

$- (x^{2} \frac{d}{d x} [e^{- x}] + e^{- x} \frac{d}{d x} [x^{2}]) + \frac{d}{d x} [2 x e^{- x}]$

Step 2.2.3

Differentiate using the chain rule, which states that $\frac{d}{d x} [f (g (x))]$ is $f' (g (x)) g' (x)$ where $f (x) = e^{x}$ and $g (x) = - x$ .

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Step 2.2.3.1

To apply the Chain Rule, set $u_{1}$ as $- x$ .

$- (x^{2} (\frac{d}{d u_{1}} [e^{u_{1}}] \frac{d}{d x} [- x]) + e^{- x} \frac{d}{d x} [x^{2}]) + \frac{d}{d x} [2 x e^{- x}]$

Step 2.2.3.2

Differentiate using the Exponential Rule which states that $\frac{d}{d u_{1}} [a^{u_{1}}]$ is $a^{u_{1}} \ln (a)$ where $a$ = $e$ .

$- (x^{2} (e^{u_{1}} \frac{d}{d x} [- x]) + e^{- x} \frac{d}{d x} [x^{2}]) + \frac{d}{d x} [2 x e^{- x}]$

Step 2.2.3.3

Replace all occurrences of $u_{1}$ with $- x$ .

$- (x^{2} (e^{- x} \frac{d}{d x} [- x]) + e^{- x} \frac{d}{d x} [x^{2}]) + \frac{d}{d x} [2 x e^{- x}]$

Step 2.2.4

Since $- 1$ is constant with respect to $x$ , the derivative of $- x$ with respect to $x$ is $- \frac{d}{d x} [x]$ .

$- (x^{2} (e^{- x} (- \frac{d}{d x} [x])) + e^{- x} \frac{d}{d x} [x^{2}]) + \frac{d}{d x} [2 x e^{- x}]$

Step 2.2.5

Differentiate using the Power Rule which states that $\frac{d}{d x} [x^{n}]$ is $n x^{n - 1}$ where $n = 1$ .

$- (x^{2} (e^{- x} (- 1 \cdot 1)) + e^{- x} \frac{d}{d x} [x^{2}]) + \frac{d}{d x} [2 x e^{- x}]$

Step 2.2.6

Differentiate using the Power Rule which states that $\frac{d}{d x} [x^{n}]$ is $n x^{n - 1}$ where $n = 2$ .

$- (x^{2} (e^{- x} (- 1 \cdot 1)) + e^{- x} (2 x)) + \frac{d}{d x} [2 x e^{- x}]$

Step 2.2.7

Multiply $- 1$ by $1$ .

$- (x^{2} (e^{- x} \cdot - 1) + e^{- x} (2 x)) + \frac{d}{d x} [2 x e^{- x}]$

Step 2.2.8

Move $- 1$ to the left of $e^{- x}$ .

$- (x^{2} (- 1 \cdot e^{- x}) + e^{- x} (2 x)) + \frac{d}{d x} [2 x e^{- x}]$

Step 2.2.9

Rewrite $- 1 e^{- x}$ as $- e^{- x}$ .

$- (x^{2} (- e^{- x}) + e^{- x} (2 x)) + \frac{d}{d x} [2 x e^{- x}]$

Step 2.3

Evaluate $\frac{d}{d x} [2 x e^{- x}]$ .

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Step 2.3.1

Since $2$ is constant with respect to $x$ , the derivative of $2 x e^{- x}$ with respect to $x$ is $2 \frac{d}{d x} [x e^{- x}]$ .

$- (x^{2} (- e^{- x}) + e^{- x} (2 x)) + 2 \frac{d}{d x} [x e^{- x}]$

Step 2.3.2

Differentiate using the Product Rule which states that $\frac{d}{d x} [f (x) g (x)]$ is $f (x) \frac{d}{d x} [g (x)] + g (x) \frac{d}{d x} [f (x)]$ where $f (x) = x$ and $g (x) = e^{- x}$ .

$- (x^{2} (- e^{- x}) + e^{- x} (2 x)) + 2 (x \frac{d}{d x} [e^{- x}] + e^{- x} \frac{d}{d x} [x])$

Step 2.3.3

Differentiate using the chain rule, which states that $\frac{d}{d x} [f (g (x))]$ is $f' (g (x)) g' (x)$ where $f (x) = e^{x}$ and $g (x) = - x$ .

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Step 2.3.3.1

To apply the Chain Rule, set $u_{2}$ as $- x$ .

$- (x^{2} (- e^{- x}) + e^{- x} (2 x)) + 2 (x (\frac{d}{d u_{2}} [e^{u_{2}}] \frac{d}{d x} [- x]) + e^{- x} \frac{d}{d x} [x])$

Step 2.3.3.2

Differentiate using the Exponential Rule which states that $\frac{d}{d u_{2}} [a^{u_{2}}]$ is $a^{u_{2}} \ln (a)$ where $a$ = $e$ .

$- (x^{2} (- e^{- x}) + e^{- x} (2 x)) + 2 (x (e^{u_{2}} \frac{d}{d x} [- x]) + e^{- x} \frac{d}{d x} [x])$

Step 2.3.3.3

Replace all occurrences of $u_{2}$ with $- x$ .

$- (x^{2} (- e^{- x}) + e^{- x} (2 x)) + 2 (x (e^{- x} \frac{d}{d x} [- x]) + e^{- x} \frac{d}{d x} [x])$

Step 2.3.4

Since $- 1$ is constant with respect to $x$ , the derivative of $- x$ with respect to $x$ is $- \frac{d}{d x} [x]$ .

$- (x^{2} (- e^{- x}) + e^{- x} (2 x)) + 2 (x (e^{- x} (- \frac{d}{d x} [x])) + e^{- x} \frac{d}{d x} [x])$

Step 2.3.5

Differentiate using the Power Rule which states that $\frac{d}{d x} [x^{n}]$ is $n x^{n - 1}$ where $n = 1$ .

$- (x^{2} (- e^{- x}) + e^{- x} (2 x)) + 2 (x (e^{- x} (- 1 \cdot 1)) + e^{- x} \frac{d}{d x} [x])$

Step 2.3.6

Differentiate using the Power Rule which states that $\frac{d}{d x} [x^{n}]$ is $n x^{n - 1}$ where $n = 1$ .

$- (x^{2} (- e^{- x}) + e^{- x} (2 x)) + 2 (x (e^{- x} (- 1 \cdot 1)) + e^{- x} \cdot 1)$

Step 2.3.7

Multiply $- 1$ by $1$ .

$- (x^{2} (- e^{- x}) + e^{- x} (2 x)) + 2 (x (e^{- x} \cdot - 1) + e^{- x} \cdot 1)$

Step 2.3.8

Move $- 1$ to the left of $e^{- x}$ .

$- (x^{2} (- e^{- x}) + e^{- x} (2 x)) + 2 (x (- 1 \cdot e^{- x}) + e^{- x} \cdot 1)$

Step 2.3.9

Rewrite $- 1 e^{- x}$ as $- e^{- x}$ .

$- (x^{2} (- e^{- x}) + e^{- x} (2 x)) + 2 (x (- e^{- x}) + e^{- x} \cdot 1)$

Step 2.3.10

Multiply $e^{- x}$ by $1$ .

$- (x^{2} (- e^{- x}) + e^{- x} (2 x)) + 2 (x (- e^{- x}) + e^{- x})$

Step 2.4

Simplify.

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Step 2.4.1

Apply the distributive property.

$- (x^{2} (- e^{- x})) - (e^{- x} (2 x)) + 2 (x (- e^{- x}) + e^{- x})$

Step 2.4.2

Apply the distributive property.

$- (x^{2} (- e^{- x})) - (e^{- x} (2 x)) + 2 (x (- e^{- x})) + 2 e^{- x}$

Step 2.4.3

Combine terms.

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Step 2.4.3.1

Multiply $- 1$ by $- 1$ .

$1 (x^{2} (e^{- x})) - (e^{- x} (2 x)) + 2 (x (- e^{- x})) + 2 e^{- x}$

Step 2.4.3.2

Multiply $x^{2}$ by $1$ .

$x^{2} e^{- x} - (e^{- x} (2 x)) + 2 (x (- e^{- x})) + 2 e^{- x}$

Step 2.4.3.3

Multiply $2$ by $- 1$ .

$x^{2} e^{- x} - 2 (e^{- x} (x)) + 2 (x (- e^{- x})) + 2 e^{- x}$

Step 2.4.3.4

Multiply $- 1$ by $2$ .

$x^{2} e^{- x} - 2 e^{- x} x - 2 (x (e^{- x})) + 2 e^{- x}$

Step 2.4.3.5

Subtract $2 x e^{- x}$ from $- 2 e^{- x} x$ .

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Step 2.4.3.5.1

Move $e^{- x}$ .

$x^{2} e^{- x} - 2 x e^{- x} - 2 x e^{- x} + 2 e^{- x}$

Step 2.4.3.5.2

Subtract $2 x e^{- x}$ from $- 2 x e^{- x}$ .

$x^{2} e^{- x} - 4 x e^{- x} + 2 e^{- x}$

Step 2.4.4

Reorder terms.

$e^{- x} x^{2} - 4 e^{- x} x + 2 e^{- x}$

Step 2.4.5

Reorder factors in $e^{- x} x^{2} - 4 e^{- x} x + 2 e^{- x}$ .

$f'' (x) = x^{2} e^{- x} - 4 x e^{- x} + 2 e^{- x}$

Step 3

Find the third derivative.

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Step 3.1

By the Sum Rule, the derivative of $x^{2} e^{- x} - 4 x e^{- x} + 2 e^{- x}$ with respect to $x$ is $\frac{d}{d x} [x^{2} e^{- x}] + \frac{d}{d x} [- 4 x e^{- x}] + \frac{d}{d x} [2 e^{- x}]$ .

$\frac{d}{d x} [x^{2} e^{- x}] + \frac{d}{d x} [- 4 x e^{- x}] + \frac{d}{d x} [2 e^{- x}]$

Step 3.2

Evaluate $\frac{d}{d x} [x^{2} e^{- x}]$ .

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Step 3.2.1

Differentiate using the Product Rule which states that $\frac{d}{d x} [f (x) g (x)]$ is $f (x) \frac{d}{d x} [g (x)] + g (x) \frac{d}{d x} [f (x)]$ where $f (x) = x^{2}$ and $g (x) = e^{- x}$ .

$x^{2} \frac{d}{d x} [e^{- x}] + e^{- x} \frac{d}{d x} [x^{2}] + \frac{d}{d x} [- 4 x e^{- x}] + \frac{d}{d x} [2 e^{- x}]$

Step 3.2.2

Differentiate using the chain rule, which states that $\frac{d}{d x} [f (g (x))]$ is $f' (g (x)) g' (x)$ where $f (x) = e^{x}$ and $g (x) = - x$ .

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Step 3.2.2.1

To apply the Chain Rule, set $u_{1}$ as $- x$ .

$x^{2} (\frac{d}{d u_{1}} [e^{u_{1}}] \frac{d}{d x} [- x]) + e^{- x} \frac{d}{d x} [x^{2}] + \frac{d}{d x} [- 4 x e^{- x}] + \frac{d}{d x} [2 e^{- x}]$

Step 3.2.2.2

Differentiate using the Exponential Rule which states that $\frac{d}{d u_{1}} [a^{u_{1}}]$ is $a^{u_{1}} \ln (a)$ where $a$ = $e$ .

$x^{2} (e^{u_{1}} \frac{d}{d x} [- x]) + e^{- x} \frac{d}{d x} [x^{2}] + \frac{d}{d x} [- 4 x e^{- x}] + \frac{d}{d x} [2 e^{- x}]$

Step 3.2.2.3

Replace all occurrences of $u_{1}$ with $- x$ .

$x^{2} (e^{- x} \frac{d}{d x} [- x]) + e^{- x} \frac{d}{d x} [x^{2}] + \frac{d}{d x} [- 4 x e^{- x}] + \frac{d}{d x} [2 e^{- x}]$

Step 3.2.3

Since $- 1$ is constant with respect to $x$ , the derivative of $- x$ with respect to $x$ is $- \frac{d}{d x} [x]$ .

$x^{2} (e^{- x} (- \frac{d}{d x} [x])) + e^{- x} \frac{d}{d x} [x^{2}] + \frac{d}{d x} [- 4 x e^{- x}] + \frac{d}{d x} [2 e^{- x}]$

Step 3.2.4

Differentiate using the Power Rule which states that $\frac{d}{d x} [x^{n}]$ is $n x^{n - 1}$ where $n = 1$ .

$x^{2} (e^{- x} (- 1 \cdot 1)) + e^{- x} \frac{d}{d x} [x^{2}] + \frac{d}{d x} [- 4 x e^{- x}] + \frac{d}{d x} [2 e^{- x}]$

Step 3.2.5

Differentiate using the Power Rule which states that $\frac{d}{d x} [x^{n}]$ is $n x^{n - 1}$ where $n = 2$ .

$x^{2} (e^{- x} (- 1 \cdot 1)) + e^{- x} (2 x) + \frac{d}{d x} [- 4 x e^{- x}] + \frac{d}{d x} [2 e^{- x}]$

Step 3.2.6

Multiply $- 1$ by $1$ .

$x^{2} (e^{- x} \cdot - 1) + e^{- x} (2 x) + \frac{d}{d x} [- 4 x e^{- x}] + \frac{d}{d x} [2 e^{- x}]$

Step 3.2.7

Move $- 1$ to the left of $e^{- x}$ .

$x^{2} (- 1 \cdot e^{- x}) + e^{- x} (2 x) + \frac{d}{d x} [- 4 x e^{- x}] + \frac{d}{d x} [2 e^{- x}]$

Step 3.2.8

Rewrite $- 1 e^{- x}$ as $- e^{- x}$ .

$x^{2} (- e^{- x}) + e^{- x} (2 x) + \frac{d}{d x} [- 4 x e^{- x}] + \frac{d}{d x} [2 e^{- x}]$

Step 3.3

Evaluate $\frac{d}{d x} [- 4 x e^{- x}]$ .

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Step 3.3.1

Since $- 4$ is constant with respect to $x$ , the derivative of $- 4 x e^{- x}$ with respect to $x$ is $- 4 \frac{d}{d x} [x e^{- x}]$ .

$x^{2} (- e^{- x}) + e^{- x} (2 x) - 4 \frac{d}{d x} [x e^{- x}] + \frac{d}{d x} [2 e^{- x}]$

Step 3.3.2

Differentiate using the Product Rule which states that $\frac{d}{d x} [f (x) g (x)]$ is $f (x) \frac{d}{d x} [g (x)] + g (x) \frac{d}{d x} [f (x)]$ where $f (x) = x$ and $g (x) = e^{- x}$ .

$x^{2} (- e^{- x}) + e^{- x} (2 x) - 4 (x \frac{d}{d x} [e^{- x}] + e^{- x} \frac{d}{d x} [x]) + \frac{d}{d x} [2 e^{- x}]$

Step 3.3.3

Differentiate using the chain rule, which states that $\frac{d}{d x} [f (g (x))]$ is $f' (g (x)) g' (x)$ where $f (x) = e^{x}$ and $g (x) = - x$ .

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Step 3.3.3.1

To apply the Chain Rule, set $u_{2}$ as $- x$ .

$x^{2} (- e^{- x}) + e^{- x} (2 x) - 4 (x (\frac{d}{d u_{2}} [e^{u_{2}}] \frac{d}{d x} [- x]) + e^{- x} \frac{d}{d x} [x]) + \frac{d}{d x} [2 e^{- x}]$

Step 3.3.3.2

Differentiate using the Exponential Rule which states that $\frac{d}{d u_{2}} [a^{u_{2}}]$ is $a^{u_{2}} \ln (a)$ where $a$ = $e$ .

$x^{2} (- e^{- x}) + e^{- x} (2 x) - 4 (x (e^{u_{2}} \frac{d}{d x} [- x]) + e^{- x} \frac{d}{d x} [x]) + \frac{d}{d x} [2 e^{- x}]$

Step 3.3.3.3

Replace all occurrences of $u_{2}$ with $- x$ .

$x^{2} (- e^{- x}) + e^{- x} (2 x) - 4 (x (e^{- x} \frac{d}{d x} [- x]) + e^{- x} \frac{d}{d x} [x]) + \frac{d}{d x} [2 e^{- x}]$

Step 3.3.4

Since $- 1$ is constant with respect to $x$ , the derivative of $- x$ with respect to $x$ is $- \frac{d}{d x} [x]$ .

$x^{2} (- e^{- x}) + e^{- x} (2 x) - 4 (x (e^{- x} (- \frac{d}{d x} [x])) + e^{- x} \frac{d}{d x} [x]) + \frac{d}{d x} [2 e^{- x}]$

Step 3.3.5

Differentiate using the Power Rule which states that $\frac{d}{d x} [x^{n}]$ is $n x^{n - 1}$ where $n = 1$ .

$x^{2} (- e^{- x}) + e^{- x} (2 x) - 4 (x (e^{- x} (- 1 \cdot 1)) + e^{- x} \frac{d}{d x} [x]) + \frac{d}{d x} [2 e^{- x}]$

Step 3.3.6

Differentiate using the Power Rule which states that $\frac{d}{d x} [x^{n}]$ is $n x^{n - 1}$ where $n = 1$ .

$x^{2} (- e^{- x}) + e^{- x} (2 x) - 4 (x (e^{- x} (- 1 \cdot 1)) + e^{- x} \cdot 1) + \frac{d}{d x} [2 e^{- x}]$

Step 3.3.7

Multiply $- 1$ by $1$ .

$x^{2} (- e^{- x}) + e^{- x} (2 x) - 4 (x (e^{- x} \cdot - 1) + e^{- x} \cdot 1) + \frac{d}{d x} [2 e^{- x}]$

Step 3.3.8

Move $- 1$ to the left of $e^{- x}$ .

$x^{2} (- e^{- x}) + e^{- x} (2 x) - 4 (x (- 1 \cdot e^{- x}) + e^{- x} \cdot 1) + \frac{d}{d x} [2 e^{- x}]$

Step 3.3.9

Rewrite $- 1 e^{- x}$ as $- e^{- x}$ .

$x^{2} (- e^{- x}) + e^{- x} (2 x) - 4 (x (- e^{- x}) + e^{- x} \cdot 1) + \frac{d}{d x} [2 e^{- x}]$

Step 3.3.10

Multiply $e^{- x}$ by $1$ .

$x^{2} (- e^{- x}) + e^{- x} (2 x) - 4 (x (- e^{- x}) + e^{- x}) + \frac{d}{d x} [2 e^{- x}]$

Step 3.4

Evaluate $\frac{d}{d x} [2 e^{- x}]$ .

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Step 3.4.1

Since $2$ is constant with respect to $x$ , the derivative of $2 e^{- x}$ with respect to $x$ is $2 \frac{d}{d x} [e^{- x}]$ .

$x^{2} (- e^{- x}) + e^{- x} (2 x) - 4 (x (- e^{- x}) + e^{- x}) + 2 \frac{d}{d x} [e^{- x}]$

Step 3.4.2

Differentiate using the chain rule, which states that $\frac{d}{d x} [f (g (x))]$ is $f' (g (x)) g' (x)$ where $f (x) = e^{x}$ and $g (x) = - x$ .

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Step 3.4.2.1

To apply the Chain Rule, set $u_{3}$ as $- x$ .

$x^{2} (- e^{- x}) + e^{- x} (2 x) - 4 (x (- e^{- x}) + e^{- x}) + 2 (\frac{d}{d u_{3}} [e^{u_{3}}] \frac{d}{d x} [- x])$

Step 3.4.2.2

Differentiate using the Exponential Rule which states that $\frac{d}{d u_{3}} [a^{u_{3}}]$ is $a^{u_{3}} \ln (a)$ where $a$ = $e$ .

$x^{2} (- e^{- x}) + e^{- x} (2 x) - 4 (x (- e^{- x}) + e^{- x}) + 2 (e^{u_{3}} \frac{d}{d x} [- x])$

Step 3.4.2.3

Replace all occurrences of $u_{3}$ with $- x$ .

$x^{2} (- e^{- x}) + e^{- x} (2 x) - 4 (x (- e^{- x}) + e^{- x}) + 2 (e^{- x} \frac{d}{d x} [- x])$

Step 3.4.3

Since $- 1$ is constant with respect to $x$ , the derivative of $- x$ with respect to $x$ is $- \frac{d}{d x} [x]$ .

$x^{2} (- e^{- x}) + e^{- x} (2 x) - 4 (x (- e^{- x}) + e^{- x}) + 2 (e^{- x} (- \frac{d}{d x} [x]))$

Step 3.4.4

Differentiate using the Power Rule which states that $\frac{d}{d x} [x^{n}]$ is $n x^{n - 1}$ where $n = 1$ .

$x^{2} (- e^{- x}) + e^{- x} (2 x) - 4 (x (- e^{- x}) + e^{- x}) + 2 (e^{- x} (- 1 \cdot 1))$

Step 3.4.5

Multiply $- 1$ by $1$ .

$x^{2} (- e^{- x}) + e^{- x} (2 x) - 4 (x (- e^{- x}) + e^{- x}) + 2 (e^{- x} \cdot - 1)$

Step 3.4.6

Move $- 1$ to the left of $e^{- x}$ .

$x^{2} (- e^{- x}) + e^{- x} (2 x) - 4 (x (- e^{- x}) + e^{- x}) + 2 (- 1 \cdot e^{- x})$

Step 3.4.7

Rewrite $- 1 e^{- x}$ as $- e^{- x}$ .

$x^{2} (- e^{- x}) + e^{- x} (2 x) - 4 (x (- e^{- x}) + e^{- x}) + 2 (- e^{- x})$

Step 3.4.8

Multiply $- 1$ by $2$ .

$x^{2} (- e^{- x}) + e^{- x} (2 x) - 4 (x (- e^{- x}) + e^{- x}) - 2 e^{- x}$

Step 3.5

Simplify.

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Step 3.5.1

Apply the distributive property.

$x^{2} (- e^{- x}) + e^{- x} (2 x) - 4 (x (- e^{- x})) - 4 e^{- x} - 2 e^{- x}$

Step 3.5.2

Combine terms.

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Step 3.5.2.1

Multiply $- 1$ by $- 4$ .

$x^{2} (- e^{- x}) + e^{- x} (2 x) + 4 (x (e^{- x})) - 4 e^{- x} - 2 e^{- x}$

Step 3.5.2.2

Add $e^{- x} (2 x)$ and $4 x e^{- x}$ .

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Step 3.5.2.2.1

Move $e^{- x}$ .

$x^{2} (- e^{- x}) + 2 x e^{- x} + 4 x e^{- x} - 4 e^{- x} - 2 e^{- x}$

Step 3.5.2.2.2

Add $2 x e^{- x}$ and $4 x e^{- x}$ .

$x^{2} (- e^{- x}) + 6 x e^{- x} - 4 e^{- x} - 2 e^{- x}$

Step 3.5.2.3

Subtract $2 e^{- x}$ from $- 4 e^{- x}$ .

$x^{2} (- e^{- x}) + 6 x e^{- x} - 6 e^{- x}$

Step 3.5.3

Reorder terms.

$- e^{- x} x^{2} + 6 e^{- x} x - 6 e^{- x}$

Step 3.5.4

Reorder factors in $- e^{- x} x^{2} + 6 e^{- x} x - 6 e^{- x}$ .

$f''' (x) = - x^{2} e^{- x} + 6 x e^{- x} - 6 e^{- x}$

Step 4

Find the fourth derivative.

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Step 4.1

By the Sum Rule, the derivative of $- x^{2} e^{- x} + 6 x e^{- x} - 6 e^{- x}$ with respect to $x$ is $\frac{d}{d x} [- x^{2} e^{- x}] + \frac{d}{d x} [6 x e^{- x}] + \frac{d}{d x} [- 6 e^{- x}]$ .

$\frac{d}{d x} [- x^{2} e^{- x}] + \frac{d}{d x} [6 x e^{- x}] + \frac{d}{d x} [- 6 e^{- x}]$

Step 4.2

Evaluate $\frac{d}{d x} [- x^{2} e^{- x}]$ .

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Step 4.2.1

Since $- 1$ is constant with respect to $x$ , the derivative of $- x^{2} e^{- x}$ with respect to $x$ is $- \frac{d}{d x} [x^{2} e^{- x}]$ .

$- \frac{d}{d x} [x^{2} e^{- x}] + \frac{d}{d x} [6 x e^{- x}] + \frac{d}{d x} [- 6 e^{- x}]$

Step 4.2.2

Differentiate using the Product Rule which states that $\frac{d}{d x} [f (x) g (x)]$ is $f (x) \frac{d}{d x} [g (x)] + g (x) \frac{d}{d x} [f (x)]$ where $f (x) = x^{2}$ and $g (x) = e^{- x}$ .

$- (x^{2} \frac{d}{d x} [e^{- x}] + e^{- x} \frac{d}{d x} [x^{2}]) + \frac{d}{d x} [6 x e^{- x}] + \frac{d}{d x} [- 6 e^{- x}]$

Step 4.2.3

Differentiate using the chain rule, which states that $\frac{d}{d x} [f (g (x))]$ is $f' (g (x)) g' (x)$ where $f (x) = e^{x}$ and $g (x) = - x$ .

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Step 4.2.3.1

To apply the Chain Rule, set $u_{1}$ as $- x$ .

$- (x^{2} (\frac{d}{d u_{1}} [e^{u_{1}}] \frac{d}{d x} [- x]) + e^{- x} \frac{d}{d x} [x^{2}]) + \frac{d}{d x} [6 x e^{- x}] + \frac{d}{d x} [- 6 e^{- x}]$

Step 4.2.3.2

Differentiate using the Exponential Rule which states that $\frac{d}{d u_{1}} [a^{u_{1}}]$ is $a^{u_{1}} \ln (a)$ where $a$ = $e$ .

$- (x^{2} (e^{u_{1}} \frac{d}{d x} [- x]) + e^{- x} \frac{d}{d x} [x^{2}]) + \frac{d}{d x} [6 x e^{- x}] + \frac{d}{d x} [- 6 e^{- x}]$

Step 4.2.3.3

Replace all occurrences of $u_{1}$ with $- x$ .

$- (x^{2} (e^{- x} \frac{d}{d x} [- x]) + e^{- x} \frac{d}{d x} [x^{2}]) + \frac{d}{d x} [6 x e^{- x}] + \frac{d}{d x} [- 6 e^{- x}]$

Step 4.2.4

Since $- 1$ is constant with respect to $x$ , the derivative of $- x$ with respect to $x$ is $- \frac{d}{d x} [x]$ .

$- (x^{2} (e^{- x} (- \frac{d}{d x} [x])) + e^{- x} \frac{d}{d x} [x^{2}]) + \frac{d}{d x} [6 x e^{- x}] + \frac{d}{d x} [- 6 e^{- x}]$

Step 4.2.5

Differentiate using the Power Rule which states that $\frac{d}{d x} [x^{n}]$ is $n x^{n - 1}$ where $n = 1$ .

$- (x^{2} (e^{- x} (- 1 \cdot 1)) + e^{- x} \frac{d}{d x} [x^{2}]) + \frac{d}{d x} [6 x e^{- x}] + \frac{d}{d x} [- 6 e^{- x}]$

Step 4.2.6

Differentiate using the Power Rule which states that $\frac{d}{d x} [x^{n}]$ is $n x^{n - 1}$ where $n = 2$ .

$- (x^{2} (e^{- x} (- 1 \cdot 1)) + e^{- x} (2 x)) + \frac{d}{d x} [6 x e^{- x}] + \frac{d}{d x} [- 6 e^{- x}]$

Step 4.2.7

Multiply $- 1$ by $1$ .

$- (x^{2} (e^{- x} \cdot - 1) + e^{- x} (2 x)) + \frac{d}{d x} [6 x e^{- x}] + \frac{d}{d x} [- 6 e^{- x}]$

Step 4.2.8

Move $- 1$ to the left of $e^{- x}$ .

$- (x^{2} (- 1 \cdot e^{- x}) + e^{- x} (2 x)) + \frac{d}{d x} [6 x e^{- x}] + \frac{d}{d x} [- 6 e^{- x}]$

Step 4.2.9

Rewrite $- 1 e^{- x}$ as $- e^{- x}$ .

$- (x^{2} (- e^{- x}) + e^{- x} (2 x)) + \frac{d}{d x} [6 x e^{- x}] + \frac{d}{d x} [- 6 e^{- x}]$

Step 4.3

Evaluate $\frac{d}{d x} [6 x e^{- x}]$ .

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Step 4.3.1

Since $6$ is constant with respect to $x$ , the derivative of $6 x e^{- x}$ with respect to $x$ is $6 \frac{d}{d x} [x e^{- x}]$ .

$- (x^{2} (- e^{- x}) + e^{- x} (2 x)) + 6 \frac{d}{d x} [x e^{- x}] + \frac{d}{d x} [- 6 e^{- x}]$

Step 4.3.2

Differentiate using the Product Rule which states that $\frac{d}{d x} [f (x) g (x)]$ is $f (x) \frac{d}{d x} [g (x)] + g (x) \frac{d}{d x} [f (x)]$ where $f (x) = x$ and $g (x) = e^{- x}$ .

$- (x^{2} (- e^{- x}) + e^{- x} (2 x)) + 6 (x \frac{d}{d x} [e^{- x}] + e^{- x} \frac{d}{d x} [x]) + \frac{d}{d x} [- 6 e^{- x}]$

Step 4.3.3

Differentiate using the chain rule, which states that $\frac{d}{d x} [f (g (x))]$ is $f' (g (x)) g' (x)$ where $f (x) = e^{x}$ and $g (x) = - x$ .

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Step 4.3.3.1

To apply the Chain Rule, set $u_{2}$ as $- x$ .

$- (x^{2} (- e^{- x}) + e^{- x} (2 x)) + 6 (x (\frac{d}{d u_{2}} [e^{u_{2}}] \frac{d}{d x} [- x]) + e^{- x} \frac{d}{d x} [x]) + \frac{d}{d x} [- 6 e^{- x}]$

Step 4.3.3.2

Differentiate using the Exponential Rule which states that $\frac{d}{d u_{2}} [a^{u_{2}}]$ is $a^{u_{2}} \ln (a)$ where $a$ = $e$ .

$- (x^{2} (- e^{- x}) + e^{- x} (2 x)) + 6 (x (e^{u_{2}} \frac{d}{d x} [- x]) + e^{- x} \frac{d}{d x} [x]) + \frac{d}{d x} [- 6 e^{- x}]$

Step 4.3.3.3

Replace all occurrences of $u_{2}$ with $- x$ .

$- (x^{2} (- e^{- x}) + e^{- x} (2 x)) + 6 (x (e^{- x} \frac{d}{d x} [- x]) + e^{- x} \frac{d}{d x} [x]) + \frac{d}{d x} [- 6 e^{- x}]$

Step 4.3.4

Since $- 1$ is constant with respect to $x$ , the derivative of $- x$ with respect to $x$ is $- \frac{d}{d x} [x]$ .

$- (x^{2} (- e^{- x}) + e^{- x} (2 x)) + 6 (x (e^{- x} (- \frac{d}{d x} [x])) + e^{- x} \frac{d}{d x} [x]) + \frac{d}{d x} [- 6 e^{- x}]$

Step 4.3.5

Differentiate using the Power Rule which states that $\frac{d}{d x} [x^{n}]$ is $n x^{n - 1}$ where $n = 1$ .

$- (x^{2} (- e^{- x}) + e^{- x} (2 x)) + 6 (x (e^{- x} (- 1 \cdot 1)) + e^{- x} \frac{d}{d x} [x]) + \frac{d}{d x} [- 6 e^{- x}]$

Step 4.3.6

Differentiate using the Power Rule which states that $\frac{d}{d x} [x^{n}]$ is $n x^{n - 1}$ where $n = 1$ .

$- (x^{2} (- e^{- x}) + e^{- x} (2 x)) + 6 (x (e^{- x} (- 1 \cdot 1)) + e^{- x} \cdot 1) + \frac{d}{d x} [- 6 e^{- x}]$

Step 4.3.7

Multiply $- 1$ by $1$ .

$- (x^{2} (- e^{- x}) + e^{- x} (2 x)) + 6 (x (e^{- x} \cdot - 1) + e^{- x} \cdot 1) + \frac{d}{d x} [- 6 e^{- x}]$

Step 4.3.8

Move $- 1$ to the left of $e^{- x}$ .

$- (x^{2} (- e^{- x}) + e^{- x} (2 x)) + 6 (x (- 1 \cdot e^{- x}) + e^{- x} \cdot 1) + \frac{d}{d x} [- 6 e^{- x}]$

Step 4.3.9

Rewrite $- 1 e^{- x}$ as $- e^{- x}$ .

$- (x^{2} (- e^{- x}) + e^{- x} (2 x)) + 6 (x (- e^{- x}) + e^{- x} \cdot 1) + \frac{d}{d x} [- 6 e^{- x}]$

Step 4.3.10

Multiply $e^{- x}$ by $1$ .

$- (x^{2} (- e^{- x}) + e^{- x} (2 x)) + 6 (x (- e^{- x}) + e^{- x}) + \frac{d}{d x} [- 6 e^{- x}]$

Step 4.4

Evaluate $\frac{d}{d x} [- 6 e^{- x}]$ .

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Step 4.4.1

Since $- 6$ is constant with respect to $x$ , the derivative of $- 6 e^{- x}$ with respect to $x$ is $- 6 \frac{d}{d x} [e^{- x}]$ .

$- (x^{2} (- e^{- x}) + e^{- x} (2 x)) + 6 (x (- e^{- x}) + e^{- x}) - 6 \frac{d}{d x} [e^{- x}]$

Step 4.4.2

Differentiate using the chain rule, which states that $\frac{d}{d x} [f (g (x))]$ is $f' (g (x)) g' (x)$ where $f (x) = e^{x}$ and $g (x) = - x$ .

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Step 4.4.2.1

To apply the Chain Rule, set $u_{3}$ as $- x$ .

$- (x^{2} (- e^{- x}) + e^{- x} (2 x)) + 6 (x (- e^{- x}) + e^{- x}) - 6 (\frac{d}{d u_{3}} [e^{u_{3}}] \frac{d}{d x} [- x])$

Step 4.4.2.2

Differentiate using the Exponential Rule which states that $\frac{d}{d u_{3}} [a^{u_{3}}]$ is $a^{u_{3}} \ln (a)$ where $a$ = $e$ .

$- (x^{2} (- e^{- x}) + e^{- x} (2 x)) + 6 (x (- e^{- x}) + e^{- x}) - 6 (e^{u_{3}} \frac{d}{d x} [- x])$

Step 4.4.2.3

Replace all occurrences of $u_{3}$ with $- x$ .

$- (x^{2} (- e^{- x}) + e^{- x} (2 x)) + 6 (x (- e^{- x}) + e^{- x}) - 6 (e^{- x} \frac{d}{d x} [- x])$

Step 4.4.3

Since $- 1$ is constant with respect to $x$ , the derivative of $- x$ with respect to $x$ is $- \frac{d}{d x} [x]$ .

$- (x^{2} (- e^{- x}) + e^{- x} (2 x)) + 6 (x (- e^{- x}) + e^{- x}) - 6 (e^{- x} (- \frac{d}{d x} [x]))$

Step 4.4.4

Differentiate using the Power Rule which states that $\frac{d}{d x} [x^{n}]$ is $n x^{n - 1}$ where $n = 1$ .

$- (x^{2} (- e^{- x}) + e^{- x} (2 x)) + 6 (x (- e^{- x}) + e^{- x}) - 6 (e^{- x} (- 1 \cdot 1))$

Step 4.4.5

Multiply $- 1$ by $1$ .

$- (x^{2} (- e^{- x}) + e^{- x} (2 x)) + 6 (x (- e^{- x}) + e^{- x}) - 6 (e^{- x} \cdot - 1)$

Step 4.4.6

Move $- 1$ to the left of $e^{- x}$ .

$- (x^{2} (- e^{- x}) + e^{- x} (2 x)) + 6 (x (- e^{- x}) + e^{- x}) - 6 (- 1 \cdot e^{- x})$

Step 4.4.7

Rewrite $- 1 e^{- x}$ as $- e^{- x}$ .

$- (x^{2} (- e^{- x}) + e^{- x} (2 x)) + 6 (x (- e^{- x}) + e^{- x}) - 6 (- e^{- x})$

Step 4.4.8

Multiply $- 1$ by $- 6$ .

$- (x^{2} (- e^{- x}) + e^{- x} (2 x)) + 6 (x (- e^{- x}) + e^{- x}) + 6 e^{- x}$

Step 4.5

Simplify.

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Step 4.5.1

Apply the distributive property.

$- (x^{2} (- e^{- x})) - (e^{- x} (2 x)) + 6 (x (- e^{- x}) + e^{- x}) + 6 e^{- x}$

Step 4.5.2

Apply the distributive property.

$- (x^{2} (- e^{- x})) - (e^{- x} (2 x)) + 6 (x (- e^{- x})) + 6 e^{- x} + 6 e^{- x}$

Step 4.5.3

Combine terms.

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Step 4.5.3.1

Multiply $- 1$ by $- 1$ .

$1 (x^{2} (e^{- x})) - (e^{- x} (2 x)) + 6 (x (- e^{- x})) + 6 e^{- x} + 6 e^{- x}$

Step 4.5.3.2

Multiply $x^{2}$ by $1$ .

$x^{2} e^{- x} - (e^{- x} (2 x)) + 6 (x (- e^{- x})) + 6 e^{- x} + 6 e^{- x}$

Step 4.5.3.3

Multiply $2$ by $- 1$ .

$x^{2} e^{- x} - 2 (e^{- x} (x)) + 6 (x (- e^{- x})) + 6 e^{- x} + 6 e^{- x}$

Step 4.5.3.4

Multiply $- 1$ by $6$ .

$x^{2} e^{- x} - 2 e^{- x} x - 6 (x (e^{- x})) + 6 e^{- x} + 6 e^{- x}$

Step 4.5.3.5

Subtract $6 x e^{- x}$ from $- 2 e^{- x} x$ .

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Step 4.5.3.5.1

Move $e^{- x}$ .

$x^{2} e^{- x} - 2 x e^{- x} - 6 x e^{- x} + 6 e^{- x} + 6 e^{- x}$

Step 4.5.3.5.2

Subtract $6 x e^{- x}$ from $- 2 x e^{- x}$ .

$x^{2} e^{- x} - 8 x e^{- x} + 6 e^{- x} + 6 e^{- x}$

Step 4.5.3.6

Add $6 e^{- x}$ and $6 e^{- x}$ .

$x^{2} e^{- x} - 8 x e^{- x} + 12 e^{- x}$

Step 4.5.4

Reorder terms.

$e^{- x} x^{2} - 8 e^{- x} x + 12 e^{- x}$

Step 4.5.5

Reorder factors in $e^{- x} x^{2} - 8 e^{- x} x + 12 e^{- x}$ .

$f^{4} (x) = x^{2} e^{- x} - 8 x e^{- x} + 12 e^{- x}$