Calculus Examples

$y = 20 \sqrt{x}$ , $(4, 40)$

Step 1

Find the first derivative and evaluate at $x = 4$ and $y = 40$ 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 $\sqrt{x}$ as $x^{\frac{1}{2}}$ .

$\frac{d}{d x} [20 x^{\frac{1}{2}}]$

Step 1.2

Since $20$ is constant with respect to $x$ , the derivative of $20 x^{\frac{1}{2}}$ with respect to $x$ is $20 \frac{d}{d x} [x^{\frac{1}{2}}]$ .

$20 \frac{d}{d x} [x^{\frac{1}{2}}]$

Step 1.3

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

$20 (\frac{1}{2} x^{\frac{1}{2} - 1})$

Step 1.4

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

$20 (\frac{1}{2} x^{\frac{1}{2} - 1 \cdot \frac{2}{2}})$

Step 1.5

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

$20 (\frac{1}{2} x^{\frac{1}{2} + \frac{- 1 \cdot 2}{2}})$

Step 1.6

Combine the numerators over the common denominator.

$20 (\frac{1}{2} x^{\frac{1 - 1 \cdot 2}{2}})$

Step 1.7

Simplify the numerator.

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Step 1.7.1

Multiply $- 1$ by $2$ .

$20 (\frac{1}{2} x^{\frac{1 - 2}{2}})$

Step 1.7.2

Subtract $2$ from $1$ .

$20 (\frac{1}{2} x^{\frac{- 1}{2}})$

Step 1.8

Move the negative in front of the fraction.

$20 (\frac{1}{2} x^{- \frac{1}{2}})$

Step 1.9

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

$20 \frac{x^{- \frac{1}{2}}}{2}$

Step 1.10

Combine $20$ and $\frac{x^{- \frac{1}{2}}}{2}$ .

$\frac{20 x^{- \frac{1}{2}}}{2}$

Step 1.11

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

$\frac{20}{2 x^{\frac{1}{2}}}$

Step 1.12

Factor $2$ out of $20$ .

$\frac{2 \cdot 10}{2 x^{\frac{1}{2}}}$

Step 1.13

Cancel the common factors.

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Step 1.13.1

Factor $2$ out of $2 x^{\frac{1}{2}}$ .

$\frac{2 \cdot 10}{2 (x^{\frac{1}{2}})}$

Step 1.13.2

Cancel the common factor.

$\frac{2 \cdot 10}{2 x^{\frac{1}{2}}}$

Step 1.13.3

Rewrite the expression.

$\frac{10}{x^{\frac{1}{2}}}$

Step 1.14

Evaluate the derivative at $x = 4$ .

$\frac{10}{{(4)}^{\frac{1}{2}}}$

Step 1.15

Simplify.

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Step 1.15.1

Simplify the denominator.

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Step 1.15.1.1

Rewrite $4$ as $2^{2}$ .

$\frac{10}{{(2^{2})}^{\frac{1}{2}}}$

Step 1.15.1.2

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

$\frac{10}{2^{2 (\frac{1}{2})}}$

Step 1.15.1.3

Cancel the common factor of $2$ .

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Step 1.15.1.3.1

Cancel the common factor.

$\frac{10}{2^{2 (\frac{1}{2})}}$

Step 1.15.1.3.2

Rewrite the expression.

$\frac{10}{2^{1}}$

Step 1.15.1.4

Evaluate the exponent.

$\frac{10}{2}$

Step 1.15.2

Divide $10$ by $2$ .

$5$

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 $5$ and a given point $(4, 40)$ 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 $m = \frac{y_{2} - y_{1}}{x_{2} - x_{1}}$ .

$y - (40) = 5 \cdot (x - (4))$

Step 2.2

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

$y - 40 = 5 \cdot (x - 4)$

Step 2.3

Solve for $y$ .

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Step 2.3.1

Simplify $5 \cdot (x - 4)$ .

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Step 2.3.1.1

Rewrite.

$y - 40 = 0 + 0 + 5 \cdot (x - 4)$

Step 2.3.1.2

Simplify by adding zeros.

$y - 40 = 5 \cdot (x - 4)$

Step 2.3.1.3

Apply the distributive property.

$y - 40 = 5 x + 5 \cdot - 4$

Step 2.3.1.4

Multiply $5$ by $- 4$ .

$y - 40 = 5 x - 20$

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 $40$ to both sides of the equation.

$y = 5 x - 20 + 40$

Step 2.3.2.2

Add $- 20$ and $40$ .

$y = 5 x + 20$

Step 3