Calculus Examples

$f (x) = \sqrt{7 x + 2}$ ,

$(2, 4)$

Step 1

Find the first derivative and evaluate at

$x = 2$ and

$y = 4$ to find the slope of the tangent line.

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Step 1.1

Use

$\sqrt[n]{a^{x}} = a^{\frac{x}{n}}$ to rewrite

$\sqrt{7 x + 2}$ as

${(7 x + 2)}^{\frac{1}{2}}$ .

$\frac{d}{d x} [{(7 x + 2)}^{\frac{1}{2}}]$

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

$f (x) = x^{\frac{1}{2}}$ and

$g (x) = 7 x + 2$ .

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Step 1.2.1

To apply the Chain Rule, set

$u$ as

$7 x + 2$ .

$\frac{d}{d u} [u^{\frac{1}{2}}] \frac{d}{d x} [7 x + 2]$

Step 1.2.2

Differentiate using the Power Rule which states that

$\frac{d}{d u} [u^{n}]$ is

$n u^{n - 1}$ where

$n = \frac{1}{2}$ .

$\frac{1}{2} u^{\frac{1}{2} - 1} \frac{d}{d x} [7 x + 2]$

Step 1.2.3

Replace all occurrences of

$u$ with

$7 x + 2$ .

$\frac{1}{2} {(7 x + 2)}^{\frac{1}{2} - 1} \frac{d}{d x} [7 x + 2]$

Step 1.3

To write

$- 1$ as a fraction with a common denominator, multiply by

$\frac{2}{2}$ .

$\frac{1}{2} {(7 x + 2)}^{\frac{1}{2} - 1 \cdot \frac{2}{2}} \frac{d}{d x} [7 x + 2]$

Step 1.4

Combine

$- 1$ and

$\frac{2}{2}$ .

$\frac{1}{2} {(7 x + 2)}^{\frac{1}{2} + \frac{- 1 \cdot 2}{2}} \frac{d}{d x} [7 x + 2]$

Step 1.5

Combine the numerators over the common denominator.

$\frac{1}{2} {(7 x + 2)}^{\frac{1 - 1 \cdot 2}{2}} \frac{d}{d x} [7 x + 2]$

Step 1.6

Simplify the numerator.

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Step 1.6.1

Multiply

$- 1$ by

$2$ .

$\frac{1}{2} {(7 x + 2)}^{\frac{1 - 2}{2}} \frac{d}{d x} [7 x + 2]$

Step 1.6.2

Subtract

$2$ from

$1$ .

$\frac{1}{2} {(7 x + 2)}^{\frac{- 1}{2}} \frac{d}{d x} [7 x + 2]$

Step 1.7

Combine fractions.

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Step 1.7.1

Move the negative in front of the fraction.

$\frac{1}{2} {(7 x + 2)}^{- \frac{1}{2}} \frac{d}{d x} [7 x + 2]$

Step 1.7.2

Combine

$\frac{1}{2}$ and

${(7 x + 2)}^{- \frac{1}{2}}$ .

$\frac{{(7 x + 2)}^{- \frac{1}{2}}}{2} \frac{d}{d x} [7 x + 2]$

Step 1.7.3

Move

${(7 x + 2)}^{- \frac{1}{2}}$ to the denominator using the negative exponent rule

$b^{- n} = \frac{1}{b^{n}}$ .

$\frac{1}{2 {(7 x + 2)}^{\frac{1}{2}}} \frac{d}{d x} [7 x + 2]$

Step 1.8

By the Sum Rule, the derivative of

$7 x + 2$ with respect to

$x$ is

$\frac{d}{d x} [7 x] + \frac{d}{d x} [2]$ .

$\frac{1}{2 {(7 x + 2)}^{\frac{1}{2}}} (\frac{d}{d x} [7 x] + \frac{d}{d x} [2])$

Step 1.9

Since

$7$ is constant with respect to

$x$ , the derivative of

$7 x$ with respect to

$x$ is

$7 \frac{d}{d x} [x]$ .

$\frac{1}{2 {(7 x + 2)}^{\frac{1}{2}}} (7 \frac{d}{d x} [x] + \frac{d}{d x} [2])$

Step 1.10

Differentiate using the Power Rule which states that

$\frac{d}{d x} [x^{n}]$ is

$n x^{n - 1}$ where

$n = 1$ .

$\frac{1}{2 {(7 x + 2)}^{\frac{1}{2}}} (7 \cdot 1 + \frac{d}{d x} [2])$

Step 1.11

Multiply

$7$ by

$1$ .

$\frac{1}{2 {(7 x + 2)}^{\frac{1}{2}}} (7 + \frac{d}{d x} [2])$

Step 1.12

Since

$2$ is constant with respect to

$x$ , the derivative of

$2$ with respect to

$x$ is

$0$ .

$\frac{1}{2 {(7 x + 2)}^{\frac{1}{2}}} (7 + 0)$

Step 1.13

Combine fractions.

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Step 1.13.1

Add

$7$ and

$0$ .

$\frac{1}{2 {(7 x + 2)}^{\frac{1}{2}}} \cdot 7$

Step 1.13.2

Combine

$\frac{1}{2 {(7 x + 2)}^{\frac{1}{2}}}$ and

$7$ .

$\frac{7}{2 {(7 x + 2)}^{\frac{1}{2}}}$

Step 1.14

Evaluate the derivative at

$x = 2$ .

$\frac{7}{2 {(7 (2) + 2)}^{\frac{1}{2}}}$

Step 1.15

Simplify.

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Step 1.15.1

Simplify the denominator.

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Step 1.15.1.1

Multiply

$7$ by

$2$ .

$\frac{7}{2 {(14 + 2)}^{\frac{1}{2}}}$

Step 1.15.1.2

Add

$14$ and

$2$ .

$\frac{7}{2 \cdot 16^{\frac{1}{2}}}$

Step 1.15.1.3

Rewrite

$16$ as

$4^{2}$ .

$\frac{7}{2 \cdot {(4^{2})}^{\frac{1}{2}}}$

Step 1.15.1.4

Apply the power rule and multiply exponents,

${(a^{m})}^{n} = a^{m n}$ .

$\frac{7}{2 \cdot 4^{2 (\frac{1}{2})}}$

Step 1.15.1.5

Cancel the common factor of

$2$ .

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Step 1.15.1.5.1

Cancel the common factor.

$\frac{7}{2 \cdot 4^{2 (\frac{1}{2})}}$

Step 1.15.1.5.2

Rewrite the expression.

$\frac{7}{2 \cdot 4^{1}}$

Step 1.15.1.6

Evaluate the exponent.

$\frac{7}{2 \cdot 4}$

Step 1.15.2

Multiply

$2$ by

$4$ .

$\frac{7}{8}$

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

$\frac{7}{8}$ and a given point

$(2, 4)$ 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

$m = \frac{y_{2} - y_{1}}{x_{2} - x_{1}}$ .

$y - (4) = \frac{7}{8} \cdot (x - (2))$

Step 2.2

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

$y - 4 = \frac{7}{8} \cdot (x - 2)$

Step 2.3

Solve for

$y$ .

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Step 2.3.1

Simplify

$\frac{7}{8} \cdot (x - 2)$ .

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Step 2.3.1.1

Rewrite.

$y - 4 = 0 + 0 + \frac{7}{8} \cdot (x - 2)$

Step 2.3.1.2

Simplify by adding zeros.

$y - 4 = \frac{7}{8} \cdot (x - 2)$

Step 2.3.1.3

Apply the distributive property.

$y - 4 = \frac{7}{8} x + \frac{7}{8} \cdot - 2$

Step 2.3.1.4

Combine

$\frac{7}{8}$ and

$x$ .

$y - 4 = \frac{7 x}{8} + \frac{7}{8} \cdot - 2$

Step 2.3.1.5

Cancel the common factor of

$2$ .

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Step 2.3.1.5.1

Factor

$2$ out of

$8$ .

$y - 4 = \frac{7 x}{8} + \frac{7}{2 (4)} \cdot - 2$

Step 2.3.1.5.2

Factor

$2$ out of

$- 2$ .

$y - 4 = \frac{7 x}{8} + \frac{7}{2 \cdot 4} \cdot (2 \cdot - 1)$

Step 2.3.1.5.3

Cancel the common factor.

$y - 4 = \frac{7 x}{8} + \frac{7}{2 \cdot 4} \cdot (2 \cdot - 1)$

Step 2.3.1.5.4

Rewrite the expression.

$y - 4 = \frac{7 x}{8} + \frac{7}{4} \cdot - 1$

Step 2.3.1.6

Combine

$\frac{7}{4}$ and

$- 1$ .

$y - 4 = \frac{7 x}{8} + \frac{7 \cdot - 1}{4}$

Step 2.3.1.7

Simplify the expression.

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Step 2.3.1.7.1

Multiply

$7$ by

$- 1$ .

$y - 4 = \frac{7 x}{8} + \frac{- 7}{4}$

Step 2.3.1.7.2

Move the negative in front of the fraction.

$y - 4 = \frac{7 x}{8} - \frac{7}{4}$

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

$4$ to both sides of the equation.

$y = \frac{7 x}{8} - \frac{7}{4} + 4$

Step 2.3.2.2

To write

$4$ as a fraction with a common denominator, multiply by

$\frac{4}{4}$ .

$y = \frac{7 x}{8} - \frac{7}{4} + 4 \cdot \frac{4}{4}$

Step 2.3.2.3

Combine

$4$ and

$\frac{4}{4}$ .

$y = \frac{7 x}{8} - \frac{7}{4} + \frac{4 \cdot 4}{4}$

Step 2.3.2.4

Combine the numerators over the common denominator.

$y = \frac{7 x}{8} + \frac{- 7 + 4 \cdot 4}{4}$

Step 2.3.2.5

Simplify the numerator.

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Step 2.3.2.5.1

Multiply

$4$ by

$4$ .

$y = \frac{7 x}{8} + \frac{- 7 + 16}{4}$

Step 2.3.2.5.2

Add

$- 7$ and

$16$ .

$y = \frac{7 x}{8} + \frac{9}{4}$

Step 2.3.3

Reorder terms.

$y = \frac{7}{8} x + \frac{9}{4}$

Step 3