Find Amplitude, Period, and Phase Shift f(x)=4cos(1/2x+pi/2)

$f (x) = 4 \cos (\frac{1}{2} x + \frac{π}{2})$

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.

$a = 4$

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

$c = - \frac{π}{2}$

$d = 0$

Step 2

Find the amplitude $| a |$ .

Amplitude: $4$

Step 3

Find the period of $4 \cos (\frac{x}{2} + \frac{π}{2})$ .

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

$\frac{2 π}{| b |}$

Replace $b$ with $\frac{1}{2}$ in the formula for period.

$\frac{2 π}{| \frac{1}{2} |}$

$\frac{1}{2}$ is approximately $0.5$ which is positive so remove the absolute value

$\frac{2 π}{\frac{1}{2}}$

Multiply the numerator by the reciprocal of the denominator.

$2 π \cdot 2$

Multiply $2$ by $2$ .

$4 π$

Step 4

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

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

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

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

Phase Shift: $\frac{- \frac{π}{2}}{\frac{1}{2}}$

Multiply the numerator by the reciprocal of the denominator.

Phase Shift: $- \frac{π}{2} \cdot 2$

Cancel the common factor of $2$ .

Move the leading negative in $- \frac{π}{2}$ into the numerator.

Phase Shift: $\frac{- π}{2} \cdot 2$

Cancel the common factor.

Phase Shift: $\frac{- π}{2} \cdot 2$

Rewrite the expression.

Phase Shift: $- π$

Step 5

List the properties of the trigonometric function.

Amplitude: $4$

Period: $4 π$

Phase Shift: $- π$ ( $π$ to the left)

Vertical Shift: None

Step 6