Calculus Examples

$f (x) = x e^{- \frac{x^{2}}{8}}$

Step 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 $f (x) = x$ and $g (x) = e^{- \frac{x^{2}}{8}}$ .

$x \frac{d}{d x} [e^{- \frac{x^{2}}{8}}] + e^{- \frac{x^{2}}{8}} \frac{d}{d x} [x]$

Step 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 $g (x) = - \frac{x^{2}}{8}$ .

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Step 2.1

To apply the Chain Rule, set $u$ as $- \frac{x^{2}}{8}$ .

$x (\frac{d}{d u} [e^{u}] \frac{d}{d x} [- \frac{x^{2}}{8}]) + e^{- \frac{x^{2}}{8}} \frac{d}{d x} [x]$

Step 2.2

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

$x (e^{u} \frac{d}{d x} [- \frac{x^{2}}{8}]) + e^{- \frac{x^{2}}{8}} \frac{d}{d x} [x]$

Step 2.3

Replace all occurrences of $u$ with $- \frac{x^{2}}{8}$ .

$x (e^{- \frac{x^{2}}{8}} \frac{d}{d x} [- \frac{x^{2}}{8}]) + e^{- \frac{x^{2}}{8}} \frac{d}{d x} [x]$

Step 3

Differentiate.

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Step 3.1

Since $- \frac{1}{8}$ is constant with respect to $x$ , the derivative of $- \frac{x^{2}}{8}$ with respect to $x$ is $- \frac{1}{8} \frac{d}{d x} [x^{2}]$ .

$x (e^{- \frac{x^{2}}{8}} (- \frac{1}{8} \frac{d}{d x} [x^{2}])) + e^{- \frac{x^{2}}{8}} \frac{d}{d x} [x]$

Step 3.2

Combine fractions.

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Step 3.2.1

Combine $e^{- \frac{x^{2}}{8}}$ and $\frac{1}{8}$ .

$x (- \frac{e^{- \frac{x^{2}}{8}}}{8} \frac{d}{d x} [x^{2}]) + e^{- \frac{x^{2}}{8}} \frac{d}{d x} [x]$

Step 3.2.2

Combine $x$ and $\frac{e^{- \frac{x^{2}}{8}}}{8}$ .

$- \frac{x e^{- \frac{x^{2}}{8}}}{8} \frac{d}{d x} [x^{2}] + e^{- \frac{x^{2}}{8}} \frac{d}{d x} [x]$

Step 3.3

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

$- \frac{x e^{- \frac{x^{2}}{8}}}{8} (2 x) + e^{- \frac{x^{2}}{8}} \frac{d}{d x} [x]$

Step 3.4

Combine fractions.

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Step 3.4.1

Multiply $2$ by $- 1$ .

$- 2 \frac{x e^{- \frac{x^{2}}{8}}}{8} x + e^{- \frac{x^{2}}{8}} \frac{d}{d x} [x]$

Step 3.4.2

Combine $- 2$ and $\frac{x e^{- \frac{x^{2}}{8}}}{8}$ .

$\frac{- 2 (x e^{- \frac{x^{2}}{8}})}{8} x + e^{- \frac{x^{2}}{8}} \frac{d}{d x} [x]$

Step 3.4.3

Combine $\frac{- 2 (x e^{- \frac{x^{2}}{8}})}{8}$ and $x$ .

$\frac{- 2 (x e^{- \frac{x^{2}}{8}}) x}{8} + e^{- \frac{x^{2}}{8}} \frac{d}{d x} [x]$

Step 4

Raise $x$ to the power of $1$ .

$\frac{- 2 (x^{1} x e^{- \frac{x^{2}}{8}})}{8} + e^{- \frac{x^{2}}{8}} \frac{d}{d x} [x]$

Step 5

Raise $x$ to the power of $1$ .

$\frac{- 2 (x^{1} x^{1} e^{- \frac{x^{2}}{8}})}{8} + e^{- \frac{x^{2}}{8}} \frac{d}{d x} [x]$

Step 6

Use the power rule $a^{m} a^{n} = a^{m + n}$ to combine exponents.

$\frac{- 2 (x^{1 + 1} e^{- \frac{x^{2}}{8}})}{8} + e^{- \frac{x^{2}}{8}} \frac{d}{d x} [x]$

Step 7

Reduce the expression by cancelling the common factors.

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Step 7.1

Add $1$ and $1$ .

$\frac{- 2 (x^{2} e^{- \frac{x^{2}}{8}})}{8} + e^{- \frac{x^{2}}{8}} \frac{d}{d x} [x]$

Step 7.2

Cancel the common factor of $- 2$ and $8$ .

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Step 7.2.1

Factor $2$ out of $- 2 x^{2} e^{- \frac{x^{2}}{8}}$ .

$\frac{2 (- x^{2} e^{- \frac{x^{2}}{8}})}{8} + e^{- \frac{x^{2}}{8}} \frac{d}{d x} [x]$

Step 7.2.2

Cancel the common factors.

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Step 7.2.2.1

Factor $2$ out of $8$ .

$\frac{2 (- x^{2} e^{- \frac{x^{2}}{8}})}{2 (4)} + e^{- \frac{x^{2}}{8}} \frac{d}{d x} [x]$

Step 7.2.2.2

Cancel the common factor.

$\frac{2 (- x^{2} e^{- \frac{x^{2}}{8}})}{2 \cdot 4} + e^{- \frac{x^{2}}{8}} \frac{d}{d x} [x]$

Step 7.2.2.3

Rewrite the expression.

$\frac{- x^{2} e^{- \frac{x^{2}}{8}}}{4} + e^{- \frac{x^{2}}{8}} \frac{d}{d x} [x]$

Step 7.3

Move the negative in front of the fraction.

$- \frac{x^{2} e^{- \frac{x^{2}}{8}}}{4} + e^{- \frac{x^{2}}{8}} \frac{d}{d x} [x]$

Step 8

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

$- \frac{x^{2} e^{- \frac{x^{2}}{8}}}{4} + e^{- \frac{x^{2}}{8}} \cdot 1$

Step 9

Multiply $e^{- \frac{x^{2}}{8}}$ by $1$ .

$- \frac{x^{2} e^{- \frac{x^{2}}{8}}}{4} + e^{- \frac{x^{2}}{8}}$