Calculus Examples

$- 8 \cos (8 x) = 0$

Step 1

Divide each term in $- 8 \cos (8 x) = 0$ by $- 8$ and simplify.

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Step 1.1

Divide each term in $- 8 \cos (8 x) = 0$ by $- 8$ .

$\frac{- 8 \cos (8 x)}{- 8} = \frac{0}{- 8}$

Step 1.2

Simplify the left side.

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Step 1.2.1

Cancel the common factor of $- 8$ .

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Step 1.2.1.1

Cancel the common factor.

$\frac{- 8 \cos (8 x)}{- 8} = \frac{0}{- 8}$

Step 1.2.1.2

Divide $\cos (8 x)$ by $1$ .

$\cos (8 x) = \frac{0}{- 8}$

Step 1.3

Simplify the right side.

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Step 1.3.1

Divide $0$ by $- 8$ .

$\cos (8 x) = 0$

Step 2

Take the inverse cosine of both sides of the equation to extract $x$ from inside the cosine.

$8 x = \arccos (0)$

Step 3

Simplify the right side.

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Step 3.1

The exact value of $\arccos (0)$ is $\frac{π}{2}$ .

$8 x = \frac{π}{2}$

Step 4

Divide each term in $8 x = \frac{π}{2}$ by $8$ and simplify.

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Step 4.1

Divide each term in $8 x = \frac{π}{2}$ by $8$ .

$\frac{8 x}{8} = \frac{\frac{π}{2}}{8}$

Step 4.2

Simplify the left side.

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Step 4.2.1

Cancel the common factor of $8$ .

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Step 4.2.1.1

Cancel the common factor.

$\frac{8 x}{8} = \frac{\frac{π}{2}}{8}$

Step 4.2.1.2

Divide $x$ by $1$ .

$x = \frac{\frac{π}{2}}{8}$

Step 4.3

Simplify the right side.

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Step 4.3.1

Multiply the numerator by the reciprocal of the denominator.

$x = \frac{π}{2} \cdot \frac{1}{8}$

Step 4.3.2

Multiply $\frac{π}{2} \cdot \frac{1}{8}$ .

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Step 4.3.2.1

Multiply $\frac{π}{2}$ by $\frac{1}{8}$ .

$x = \frac{π}{2 \cdot 8}$

Step 4.3.2.2

Multiply $2$ by $8$ .

$x = \frac{π}{16}$

Step 5

The cosine function is positive in the first and fourth quadrants. To find the second solution, subtract the reference angle from $2 π$ to find the solution in the fourth quadrant.

$8 x = 2 π - \frac{π}{2}$

Step 6

Solve for $x$ .

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Step 6.1

Simplify.

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Step 6.1.1

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

$8 x = 2 π \cdot \frac{2}{2} - \frac{π}{2}$

Step 6.1.2

Combine $2 π$ and $\frac{2}{2}$ .

$8 x = \frac{2 π \cdot 2}{2} - \frac{π}{2}$

Step 6.1.3

Combine the numerators over the common denominator.

$8 x = \frac{2 π \cdot 2 - π}{2}$

Step 6.1.4

Multiply $2$ by $2$ .

$8 x = \frac{4 π - π}{2}$

Step 6.1.5

Subtract $π$ from $4 π$ .

$8 x = \frac{3 π}{2}$

Step 6.2

Divide each term in $8 x = \frac{3 π}{2}$ by $8$ and simplify.

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Step 6.2.1

Divide each term in $8 x = \frac{3 π}{2}$ by $8$ .

$\frac{8 x}{8} = \frac{\frac{3 π}{2}}{8}$

Step 6.2.2

Simplify the left side.

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Step 6.2.2.1

Cancel the common factor of $8$ .

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Step 6.2.2.1.1

Cancel the common factor.

$\frac{8 x}{8} = \frac{\frac{3 π}{2}}{8}$

Step 6.2.2.1.2

Divide $x$ by $1$ .

$x = \frac{\frac{3 π}{2}}{8}$

Step 6.2.3

Simplify the right side.

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Step 6.2.3.1

Multiply the numerator by the reciprocal of the denominator.

$x = \frac{3 π}{2} \cdot \frac{1}{8}$

Step 6.2.3.2

Multiply $\frac{3 π}{2} \cdot \frac{1}{8}$ .

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Step 6.2.3.2.1

Multiply $\frac{3 π}{2}$ by $\frac{1}{8}$ .

$x = \frac{3 π}{2 \cdot 8}$

Step 6.2.3.2.2

Multiply $2$ by $8$ .

$x = \frac{3 π}{16}$

Step 7

Find the period of $\cos (8 x)$ .

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Step 7.1

The period of the function can be calculated using $\frac{2 π}{| b |}$ .

$\frac{2 π}{| b |}$

Step 7.2

Replace $b$ with $8$ in the formula for period.

$\frac{2 π}{| 8 |}$

Step 7.3

The absolute value is the distance between a number and zero. The distance between $0$ and $8$ is $8$ .

$\frac{2 π}{8}$

Step 7.4

Cancel the common factor of $2$ and $8$ .

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Step 7.4.1

Factor $2$ out of $2 π$ .

$\frac{2 (π)}{8}$

Step 7.4.2

Cancel the common factors.

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Step 7.4.2.1

Factor $2$ out of $8$ .

$\frac{2 π}{2 \cdot 4}$

Step 7.4.2.2

Cancel the common factor.

$\frac{2 π}{2 \cdot 4}$

Step 7.4.2.3

Rewrite the expression.

$\frac{π}{4}$

Step 8

The period of the $\cos (8 x)$ function is $\frac{π}{4}$ so values will repeat every $\frac{π}{4}$ radians in both directions.

$x = \frac{π}{16} + \frac{π n}{4}, \frac{3 π}{16} + \frac{π n}{4}$ , for any integer $n$

Step 9

Consolidate the answers.

$x = \frac{π}{16} + \frac{π n}{8}$ , for any integer $n$