Calculus Examples

$f (x) = \frac{4}{x}$ at $(8, \frac{1}{2})$

Step 1

Find the first derivative and evaluate at $x = 8$ and $y = \frac{1}{2}$ to find the slope of the tangent line.

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Step 1.1

Since $4$ is constant with respect to $x$ , the derivative of $\frac{4}{x}$ with respect to $x$ is $4 \frac{d}{d x} [\frac{1}{x}]$ .

$4 \frac{d}{d x} [\frac{1}{x}]$

Step 1.2

Rewrite $\frac{1}{x}$ as $x^{- 1}$ .

$4 \frac{d}{d x} [x^{- 1}]$

Step 1.3

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

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

Step 1.4

Multiply $- 1$ by $4$ .

$- 4 x^{- 2}$

Step 1.5

Simplify.

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Step 1.5.1

Rewrite the expression using the negative exponent rule $b^{- n} = \frac{1}{b^{n}}$ .

$- 4 \frac{1}{x^{2}}$

Step 1.5.2

Combine terms.

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Step 1.5.2.1

Combine $- 4$ and $\frac{1}{x^{2}}$ .

$\frac{- 4}{x^{2}}$

Step 1.5.2.2

Move the negative in front of the fraction.

$- \frac{4}{x^{2}}$

Step 1.6

Evaluate the derivative at $x = 8$ .

$- \frac{4}{{(8)}^{2}}$

Step 1.7

Simplify.

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Step 1.7.1

Raise $8$ to the power of $2$ .

$- \frac{4}{64}$

Step 1.7.2

Cancel the common factor of $4$ and $64$ .

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Step 1.7.2.1

Factor $4$ out of $4$ .

$- \frac{4 (1)}{64}$

Step 1.7.2.2

Cancel the common factors.

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Step 1.7.2.2.1

Factor $4$ out of $64$ .

$- \frac{4 \cdot 1}{4 \cdot 16}$

Step 1.7.2.2.2

Cancel the common factor.

$- \frac{4 \cdot 1}{4 \cdot 16}$

Step 1.7.2.2.3

Rewrite the expression.

$- \frac{1}{16}$

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 $- \frac{1}{16}$ and a given point $(8, \frac{1}{2})$ 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 $m = \frac{y_{2} - y_{1}}{x_{2} - x_{1}}$ .

$y - (\frac{1}{2}) = - \frac{1}{16} \cdot (x - (8))$

Step 2.2

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

$y - \frac{1}{2} = - \frac{1}{16} \cdot (x - 8)$

Step 2.3

Solve for $y$ .

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Step 2.3.1

Simplify $- \frac{1}{16} \cdot (x - 8)$ .

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Step 2.3.1.1

Rewrite.

$y - \frac{1}{2} = 0 + 0 - \frac{1}{16} \cdot (x - 8)$

Step 2.3.1.2

Simplify by adding zeros.

$y - \frac{1}{2} = - \frac{1}{16} \cdot (x - 8)$

Step 2.3.1.3

Apply the distributive property.

$y - \frac{1}{2} = - \frac{1}{16} x - \frac{1}{16} \cdot - 8$

Step 2.3.1.4

Combine $x$ and $\frac{1}{16}$ .

$y - \frac{1}{2} = - \frac{x}{16} - \frac{1}{16} \cdot - 8$

Step 2.3.1.5

Cancel the common factor of $8$ .

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Step 2.3.1.5.1

Move the leading negative in $- \frac{1}{16}$ into the numerator.

$y - \frac{1}{2} = - \frac{x}{16} + \frac{- 1}{16} \cdot - 8$

Step 2.3.1.5.2

Factor $8$ out of $16$ .

$y - \frac{1}{2} = - \frac{x}{16} + \frac{- 1}{8 (2)} \cdot - 8$

Step 2.3.1.5.3

Factor $8$ out of $- 8$ .

$y - \frac{1}{2} = - \frac{x}{16} + \frac{- 1}{8 \cdot 2} \cdot (8 \cdot - 1)$

Step 2.3.1.5.4

Cancel the common factor.

$y - \frac{1}{2} = - \frac{x}{16} + \frac{- 1}{8 \cdot 2} \cdot (8 \cdot - 1)$

Step 2.3.1.5.5

Rewrite the expression.

$y - \frac{1}{2} = - \frac{x}{16} + \frac{- 1}{2} \cdot - 1$

Step 2.3.1.6

Combine $\frac{- 1}{2}$ and $- 1$ .

$y - \frac{1}{2} = - \frac{x}{16} + \frac{- - 1}{2}$

Step 2.3.1.7

Multiply $- 1$ by $- 1$ .

$y - \frac{1}{2} = - \frac{x}{16} + \frac{1}{2}$

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

Add $\frac{1}{2}$ to both sides of the equation.

$y = - \frac{x}{16} + \frac{1}{2} + \frac{1}{2}$

Step 2.3.2.2

Combine the numerators over the common denominator.

$y = \frac{- x}{16} + \frac{1 + 1}{2}$

Step 2.3.2.3

Add $1$ and $1$ .

$y = \frac{- x}{16} + \frac{2}{2}$

Step 2.3.2.4

Simplify each term.

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Step 2.3.2.4.1

Move the negative in front of the fraction.

$y = - \frac{x}{16} + \frac{2}{2}$

Step 2.3.2.4.2

Divide $2$ by $2$ .

$y = - \frac{x}{16} + 1$

Step 2.3.3

Write in $y = m x + b$ form.

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Step 2.3.3.1

Reorder terms.

$y = - (\frac{1}{16} x) + 1$

Step 2.3.3.2

Remove parentheses.

$y = - \frac{1}{16} x + 1$

Step 3