Trigonometry Examples

$f (x) = - 4 \cos (5 x - 9) - 7$

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.

$a = - 4$

$b = 5$

$c = 9$

$d = - 7$

Step 2

Find the amplitude $| a |$ .

Amplitude: $4$

Step 3

Find the period using the formula $\frac{2 π}{| b |}$ .

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Step 3.1

Find the period of $- 4 \cos (5 x - 9)$ .

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Step 3.1.1

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

$\frac{2 π}{| b |}$

Step 3.1.2

Replace $b$ with $5$ in the formula for period.

$\frac{2 π}{| 5 |}$

Step 3.1.3

The absolute value is the distance between a number and zero. The distance between $0$ and $5$ is $5$ .

$\frac{2 π}{5}$

Step 3.2

Find the period of $- 7$ .

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Step 3.2.1

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

$\frac{2 π}{| b |}$

Step 3.2.2

Replace $b$ with $5$ in the formula for period.

$\frac{2 π}{| 5 |}$

Step 3.2.3

The absolute value is the distance between a number and zero. The distance between $0$ and $5$ is $5$ .

$\frac{2 π}{5}$

Step 3.3

The period of addition/subtraction of trig functions is the maximum of the individual periods.

$\frac{2 π}{5}$

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: $\frac{9}{5}$

Step 5

List the properties of the trigonometric function.

Amplitude: $4$

Period: $\frac{2 π}{5}$

Phase Shift: $\frac{9}{5}$ ( $\frac{9}{5}$ to the right)

Vertical Shift: $- 7$

Step 6