Calculus Examples

$f (x) = \sqrt{x + 9}$ at the point where $x = 0$

Step 1

Find the corresponding $y$ -value to $x = 0$ .

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Step 1.1

Substitute $0$ in for $x$ .

$y = \sqrt{(0) + 9}$

Step 1.2

Simplify $\sqrt{(0) + 9}$ .

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Step 1.2.1

Add $0$ and $9$ .

$y = \sqrt{9}$

Step 1.2.2

Rewrite $9$ as $3^{2}$ .

$y = \sqrt{3^{2}}$

Step 1.2.3

Pull terms out from under the radical, assuming positive real numbers.

$y = 3$

Step 2

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 2.1

Use $\sqrt[n]{a^{x}} = a^{\frac{x}{n}}$ to rewrite $\sqrt{x + 9}$ as ${(x + 9)}^{\frac{1}{2}}$ .

$\frac{d}{d x} [{(x + 9)}^{\frac{1}{2}}]$

Step 2.2

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 $g (x) = x + 9$ .

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Step 2.2.1

To apply the Chain Rule, set $u$ as $x + 9$ .

$\frac{d}{d u} [u^{\frac{1}{2}}] \frac{d}{d x} [x + 9]$

Step 2.2.2

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

$\frac{1}{2} u^{\frac{1}{2} - 1} \frac{d}{d x} [x + 9]$

Step 2.2.3

Replace all occurrences of $u$ with $x + 9$ .

$\frac{1}{2} {(x + 9)}^{\frac{1}{2} - 1} \frac{d}{d x} [x + 9]$

Step 2.3

To write $- 1$ as a fraction with a common denominator, multiply by $\frac{2}{2}$ .

$\frac{1}{2} {(x + 9)}^{\frac{1}{2} - 1 \cdot \frac{2}{2}} \frac{d}{d x} [x + 9]$

Step 2.4

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

$\frac{1}{2} {(x + 9)}^{\frac{1}{2} + \frac{- 1 \cdot 2}{2}} \frac{d}{d x} [x + 9]$

Step 2.5

Combine the numerators over the common denominator.

$\frac{1}{2} {(x + 9)}^{\frac{1 - 1 \cdot 2}{2}} \frac{d}{d x} [x + 9]$

Step 2.6

Simplify the numerator.

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Step 2.6.1

Multiply $- 1$ by $2$ .

$\frac{1}{2} {(x + 9)}^{\frac{1 - 2}{2}} \frac{d}{d x} [x + 9]$

Step 2.6.2

Subtract $2$ from $1$ .

$\frac{1}{2} {(x + 9)}^{\frac{- 1}{2}} \frac{d}{d x} [x + 9]$

Step 2.7

Combine fractions.

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Step 2.7.1

Move the negative in front of the fraction.

$\frac{1}{2} {(x + 9)}^{- \frac{1}{2}} \frac{d}{d x} [x + 9]$

Step 2.7.2

Combine $\frac{1}{2}$ and ${(x + 9)}^{- \frac{1}{2}}$ .

$\frac{{(x + 9)}^{- \frac{1}{2}}}{2} \frac{d}{d x} [x + 9]$

Step 2.7.3

Move ${(x + 9)}^{- \frac{1}{2}}$ to the denominator using the negative exponent rule $b^{- n} = \frac{1}{b^{n}}$ .

$\frac{1}{2 {(x + 9)}^{\frac{1}{2}}} \frac{d}{d x} [x + 9]$

Step 2.8

By the Sum Rule, the derivative of $x + 9$ with respect to $x$ is $\frac{d}{d x} [x] + \frac{d}{d x} [9]$ .

$\frac{1}{2 {(x + 9)}^{\frac{1}{2}}} (\frac{d}{d x} [x] + \frac{d}{d x} [9])$

Step 2.9

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

$\frac{1}{2 {(x + 9)}^{\frac{1}{2}}} (1 + \frac{d}{d x} [9])$

Step 2.10

Since $9$ is constant with respect to $x$ , the derivative of $9$ with respect to $x$ is $0$ .

$\frac{1}{2 {(x + 9)}^{\frac{1}{2}}} (1 + 0)$

Step 2.11

Simplify the expression.

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Step 2.11.1

Add $1$ and $0$ .

$\frac{1}{2 {(x + 9)}^{\frac{1}{2}}} \cdot 1$

Step 2.11.2

Multiply $\frac{1}{2 {(x + 9)}^{\frac{1}{2}}}$ by $1$ .

$\frac{1}{2 {(x + 9)}^{\frac{1}{2}}}$

Step 2.12

Evaluate the derivative at $x = 0$ .

$\frac{1}{2 {((0) + 9)}^{\frac{1}{2}}}$

Step 2.13

Simplify.

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Step 2.13.1

Simplify the denominator.

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Step 2.13.1.1

Add $0$ and $9$ .

$\frac{1}{2 \cdot 9^{\frac{1}{2}}}$

Step 2.13.1.2

Rewrite $9$ as $3^{2}$ .

$\frac{1}{2 \cdot {(3^{2})}^{\frac{1}{2}}}$

Step 2.13.1.3

Apply the power rule and multiply exponents, ${(a^{m})}^{n} = a^{m n}$ .

$\frac{1}{2 \cdot 3^{2 (\frac{1}{2})}}$

Step 2.13.1.4

Cancel the common factor of $2$ .

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Step 2.13.1.4.1

Cancel the common factor.

$\frac{1}{2 \cdot 3^{2 (\frac{1}{2})}}$

Step 2.13.1.4.2

Rewrite the expression.

$\frac{1}{2 \cdot 3^{1}}$

Step 2.13.1.5

Evaluate the exponent.

$\frac{1}{2 \cdot 3}$

Step 2.13.2

Multiply $2$ by $3$ .

$\frac{1}{6}$

Step 3

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

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Step 3.1

Use the slope $\frac{1}{6}$ 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 $m = \frac{y_{2} - y_{1}}{x_{2} - x_{1}}$ .

$y - (3) = \frac{1}{6} \cdot (x - (0))$

Step 3.2

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

$y - 3 = \frac{1}{6} \cdot (x + 0)$

Step 3.3

Solve for $y$ .

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Step 3.3.1

Simplify $\frac{1}{6} \cdot (x + 0)$ .

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Step 3.3.1.1

Add $x$ and $0$ .

$y - 3 = \frac{1}{6} \cdot x$

Step 3.3.1.2

Combine $\frac{1}{6}$ and $x$ .

$y - 3 = \frac{x}{6}$

Step 3.3.2

Add $3$ to both sides of the equation.

$y = \frac{x}{6} + 3$

Step 3.3.3

Reorder terms.

$y = \frac{1}{6} x + 3$

Step 4