Calculus Examples

$y = 2 x^{3} - 5 x$ , $(1, - 3)$

Step 1

Find the first derivative and evaluate at $x = 1$ and $y = - 3$ to find the slope of the tangent line.

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Step 1.1

By the Sum Rule, the derivative of $2 x^{3} - 5 x$ with respect to $x$ is $\frac{d}{d x} [2 x^{3}] + \frac{d}{d x} [- 5 x]$ .

$\frac{d}{d x} [2 x^{3}] + \frac{d}{d x} [- 5 x]$

Step 1.2

Evaluate $\frac{d}{d x} [2 x^{3}]$ .

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Step 1.2.1

Since $2$ is constant with respect to $x$ , the derivative of $2 x^{3}$ with respect to $x$ is $2 \frac{d}{d x} [x^{3}]$ .

$2 \frac{d}{d x} [x^{3}] + \frac{d}{d x} [- 5 x]$

Step 1.2.2

Differentiate using the Power Rule which states that $\frac{d}{d x} [x^{n}]$ is $n x^{n - 1}$ where $n = 3$ .

$2 (3 x^{2}) + \frac{d}{d x} [- 5 x]$

Step 1.2.3

Multiply $3$ by $2$ .

$6 x^{2} + \frac{d}{d x} [- 5 x]$

Step 1.3

Evaluate $\frac{d}{d x} [- 5 x]$ .

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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 $- 5 \frac{d}{d x} [x]$ .

$6 x^{2} - 5 \frac{d}{d x} [x]$

Step 1.3.2

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

$6 x^{2} - 5 \cdot 1$

Step 1.3.3

Multiply $- 5$ by $1$ .

$6 x^{2} - 5$

Step 1.4

Evaluate the derivative at $x = 1$ .

$6 {(1)}^{2} - 5$

Step 1.5

Simplify.

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Step 1.5.1

Simplify each term.

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Step 1.5.1.1

One to any power is one.

$6 \cdot 1 - 5$

Step 1.5.1.2

Multiply $6$ by $1$ .

$6 - 5$

Step 1.5.2

Subtract $5$ from $6$ .

$1$

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 $1$ and a given point $(1, - 3)$ 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 $m = \frac{y_{2} - y_{1}}{x_{2} - x_{1}}$ .

$y - (- 3) = 1 \cdot (x - (1))$

Step 2.2

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

$y + 3 = 1 \cdot (x - 1)$

Step 2.3

Solve for $y$ .

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Step 2.3.1

Multiply $x - 1$ by $1$ .

$y + 3 = x - 1$

Step 2.3.2

Move all terms not containing $y$ to the right side of the equation.

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Step 2.3.2.1

Subtract $3$ from both sides of the equation.

$y = x - 1 - 3$

Step 2.3.2.2

Subtract $3$ from $- 1$ .

$y = x - 4$

Step 3