Calculus Examples

$g (x) = 3 e^{- 5 x}$ at the point $(0, 3)$

Step 1

Find the first derivative and evaluate at $x = 0$ and $y = 3$ to find the slope of the tangent line.

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Step 1.1

Since $3$ is constant with respect to $x$ , the derivative of $3 e^{- 5 x}$ with respect to $x$ is $3 \frac{d}{d x} [e^{- 5 x}]$ .

$3 \frac{d}{d x} [e^{- 5 x}]$

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 $g (x) = - 5 x$ .

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Step 1.2.1

To apply the Chain Rule, set $u$ as $- 5 x$ .

$3 (\frac{d}{d u} [e^{u}] \frac{d}{d x} [- 5 x])$

Step 1.2.2

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

$3 (e^{u} \frac{d}{d x} [- 5 x])$

Step 1.2.3

Replace all occurrences of $u$ with $- 5 x$ .

$3 (e^{- 5 x} \frac{d}{d x} [- 5 x])$

Step 1.3

Differentiate.

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Step 1.3.1

Since $- 5$ is constant with respect to $x$ , the derivative of $- 5 x$ with respect to $x$ is $- 5 \frac{d}{d x} [x]$ .

$3 e^{- 5 x} (- 5 \frac{d}{d x} [x])$

Step 1.3.2

Multiply $- 5$ by $3$ .

$- 15 e^{- 5 x} \frac{d}{d x} [x]$

Step 1.3.3

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

$- 15 e^{- 5 x} \cdot 1$

Step 1.3.4

Multiply $- 15$ by $1$ .

$- 15 e^{- 5 x}$

Step 1.4

Evaluate the derivative at $x = 0$ .

$- 15 e^{- 5 \cdot 0}$

Step 1.5

Simplify.

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Step 1.5.1

Multiply $- 5$ by $0$ .

$- 15 e^{0}$

Step 1.5.2

Anything raised to $0$ is $1$ .

$- 15 \cdot 1$

Step 1.5.3

Multiply $- 15$ by $1$ .

$- 15$

Step 2

Plug the slope and point values into the point-slope formula and solve for $y$ .

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Step 2.1

Use the slope $- 15$ and a given point $(0, 3)$ to substitute for $x_{1}$ and $y_{1}$ in the point-slope form $y - y_{1} = m (x - x_{1})$ , which is derived from the slope equation $m = \frac{y_{2} - y_{1}}{x_{2} - x_{1}}$ .

$y - (3) = - 15 \cdot (x - (0))$

Step 2.2

Simplify the equation and keep it in point-slope form.

$y - 3 = - 15 \cdot (x + 0)$

Step 2.3

Solve for $y$ .

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Step 2.3.1

Add $x$ and $0$ .

$y - 3 = - 15 x$

Step 2.3.2

Add $3$ to both sides of the equation.

$y = - 15 x + 3$

Step 3