Precalculus Examples

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

Step 1

Use the form $a \cos (b x - c) + d$ to find the variables used to find the amplitude, period, phase shift, and vertical shift.

$a = \frac{1}{2}$

$b = 8$

$c = 0$

$d = 0$

Step 2

Find the amplitude $| a |$ .

Amplitude: $\frac{1}{2}$

Step 3

Find the period of $\frac{\cos (8 x)}{2}$ .

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Step 3.1

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

$\frac{2 π}{| b |}$

Step 3.2

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

$\frac{2 π}{| 8 |}$

Step 3.3

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

$\frac{2 π}{8}$

Step 3.4

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

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Step 3.4.1

Factor $2$ out of $2 π$ .

$\frac{2 (π)}{8}$

Step 3.4.2

Cancel the common factors.

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Step 3.4.2.1

Factor $2$ out of $8$ .

$\frac{2 π}{2 \cdot 4}$

Step 3.4.2.2

Cancel the common factor.

$\frac{2 π}{2 \cdot 4}$

Step 3.4.2.3

Rewrite the expression.

$\frac{π}{4}$

Step 4

Find the phase shift using the formula $\frac{c}{b}$ .

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Step 4.1

The phase shift of the function can be calculated from $\frac{c}{b}$ .

Phase Shift: $\frac{c}{b}$

Step 4.2

Replace the values of $c$ and $b$ in the equation for phase shift.

Phase Shift: $\frac{0}{8}$

Step 4.3

Divide $0$ by $8$ .

Phase Shift: $0$

Step 5

List the properties of the trigonometric function.

Amplitude: $\frac{1}{2}$

Period: $\frac{π}{4}$

Phase Shift: None

Vertical Shift: None

Step 6

Select a few points to graph.

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Step 6.1

Find the point at $x = 0$ .

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Step 6.1.1

Replace the variable $x$ with $0$ in the expression.

$f (0) = \frac{\cos (8 (0))}{2}$

Step 6.1.2

Simplify the result.

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Step 6.1.2.1

Simplify the numerator.

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Step 6.1.2.1.1

Multiply $8$ by $0$ .

$f (0) = \frac{\cos (0)}{2}$

Step 6.1.2.1.2

The exact value of $\cos (0)$ is $1$ .

$f (0) = \frac{1}{2}$

Step 6.1.2.2

The final answer is $\frac{1}{2}$ .

$\frac{1}{2}$

Step 6.2

Find the point at $x = \frac{π}{16}$ .

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Step 6.2.1

Replace the variable $x$ with $\frac{π}{16}$ in the expression.

$f (\frac{π}{16}) = \frac{\cos (8 (\frac{π}{16}))}{2}$

Step 6.2.2

Simplify the result.

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Step 6.2.2.1

Simplify the numerator.

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Step 6.2.2.1.1

Cancel the common factor of $8$ .

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Step 6.2.2.1.1.1

Factor $8$ out of $16$ .

$f (\frac{π}{16}) = \frac{\cos (8 (\frac{π}{8 (2)}))}{2}$

Step 6.2.2.1.1.2

Cancel the common factor.

$f (\frac{π}{16}) = \frac{\cos (8 (\frac{π}{8 \cdot 2}))}{2}$

Step 6.2.2.1.1.3

Rewrite the expression.

$f (\frac{π}{16}) = \frac{\cos (\frac{π}{2})}{2}$

Step 6.2.2.1.2

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

$f (\frac{π}{16}) = \frac{0}{2}$

Step 6.2.2.2

Divide $0$ by $2$ .

$f (\frac{π}{16}) = 0$

Step 6.2.2.3

The final answer is $0$ .

$0$

Step 6.3

Find the point at $x = \frac{π}{8}$ .

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Step 6.3.1

Replace the variable $x$ with $\frac{π}{8}$ in the expression.

$f (\frac{π}{8}) = \frac{\cos (8 (\frac{π}{8}))}{2}$

Step 6.3.2

Simplify the result.

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Step 6.3.2.1

Simplify the numerator.

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Step 6.3.2.1.1

Cancel the common factor of $8$ .

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Step 6.3.2.1.1.1

Cancel the common factor.

$f (\frac{π}{8}) = \frac{\cos (8 (\frac{π}{8}))}{2}$

Step 6.3.2.1.1.2

Rewrite the expression.

$f (\frac{π}{8}) = \frac{\cos (π)}{2}$

Step 6.3.2.1.2

Apply the reference angle by finding the angle with equivalent trig values in the first quadrant. Make the expression negative because cosine is negative in the second quadrant.

$f (\frac{π}{8}) = \frac{- \cos (0)}{2}$

Step 6.3.2.1.3

The exact value of $\cos (0)$ is $1$ .

$f (\frac{π}{8}) = \frac{- 1 \cdot 1}{2}$

Step 6.3.2.1.4

Multiply $- 1$ by $1$ .

$f (\frac{π}{8}) = \frac{- 1}{2}$

Step 6.3.2.2

Move the negative in front of the fraction.

$f (\frac{π}{8}) = - \frac{1}{2}$

Step 6.3.2.3

The final answer is $- \frac{1}{2}$ .

$- \frac{1}{2}$

Step 6.4

Find the point at $x = \frac{3 π}{16}$ .

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Step 6.4.1

Replace the variable $x$ with $\frac{3 π}{16}$ in the expression.

$f (\frac{3 π}{16}) = \frac{\cos (8 (\frac{3 π}{16}))}{2}$

Step 6.4.2

Simplify the result.

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Step 6.4.2.1

Simplify the numerator.

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Step 6.4.2.1.1

Cancel the common factor of $8$ .

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Step 6.4.2.1.1.1

Factor $8$ out of $16$ .

$f (\frac{3 π}{16}) = \frac{\cos (8 (\frac{3 π}{8 (2)}))}{2}$

Step 6.4.2.1.1.2

Cancel the common factor.

$f (\frac{3 π}{16}) = \frac{\cos (8 (\frac{3 π}{8 \cdot 2}))}{2}$

Step 6.4.2.1.1.3

Rewrite the expression.

$f (\frac{3 π}{16}) = \frac{\cos (\frac{3 π}{2})}{2}$

Step 6.4.2.1.2

Apply the reference angle by finding the angle with equivalent trig values in the first quadrant.

$f (\frac{3 π}{16}) = \frac{\cos (\frac{π}{2})}{2}$

Step 6.4.2.1.3

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

$f (\frac{3 π}{16}) = \frac{0}{2}$

Step 6.4.2.2

Divide $0$ by $2$ .

$f (\frac{3 π}{16}) = 0$

Step 6.4.2.3

The final answer is $0$ .

$0$

Step 6.5

Find the point at $x = \frac{π}{4}$ .

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Step 6.5.1

Replace the variable $x$ with $\frac{π}{4}$ in the expression.

$f (\frac{π}{4}) = \frac{\cos (8 (\frac{π}{4}))}{2}$

Step 6.5.2

Simplify the result.

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Step 6.5.2.1

Simplify the numerator.

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Step 6.5.2.1.1

Cancel the common factor of $4$ .

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Step 6.5.2.1.1.1

Factor $4$ out of $8$ .

$f (\frac{π}{4}) = \frac{\cos (4 (2) (\frac{π}{4}))}{2}$

Step 6.5.2.1.1.2

Cancel the common factor.

$f (\frac{π}{4}) = \frac{\cos (4 \cdot (2 (\frac{π}{4})))}{2}$

Step 6.5.2.1.1.3

Rewrite the expression.

$f (\frac{π}{4}) = \frac{\cos (2 π)}{2}$

Step 6.5.2.1.2

Subtract full rotations of $2 π$ until the angle is greater than or equal to $0$ and less than $2 π$ .

$f (\frac{π}{4}) = \frac{\cos (0)}{2}$

Step 6.5.2.1.3

The exact value of $\cos (0)$ is $1$ .

$f (\frac{π}{4}) = \frac{1}{2}$

Step 6.5.2.2

The final answer is $\frac{1}{2}$ .

$\frac{1}{2}$

Step 6.6

List the points in a table.

$\begin{array}{c} x & f (x) \\ 0 & \frac{1}{2} \\ \frac{π}{16} & 0 \\ \frac{π}{8} & - \frac{1}{2} \\ \frac{3 π}{16} & 0 \\ \frac{π}{4} & \frac{1}{2} \end{array}$

Step 7

The trig function can be graphed using the amplitude, period, phase shift, vertical shift, and the points.

Amplitude: $\frac{1}{2}$

Period: $\frac{π}{4}$

Phase Shift: None

Vertical Shift: None

$\begin{array}{c} x & f (x) \\ 0 & \frac{1}{2} \\ \frac{π}{16} & 0 \\ \frac{π}{8} & - \frac{1}{2} \\ \frac{3 π}{16} & 0 \\ \frac{π}{4} & \frac{1}{2} \end{array}$

Step 8