Trigonometry Examples

$y = \frac{7}{4} \cdot \cos (- \frac{4 π}{5} x)$

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.

$a = \frac{7}{4}$

$b = \frac{4 π}{5}$

$c = 0$

$d = 0$

Step 2

Find the amplitude $| a |$ .

Amplitude: $\frac{7}{4}$

Step 3

Find the period of $\frac{7 \cos (\frac{4 x π}{5})}{4}$ .

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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 $\frac{4 π}{5}$ in the formula for period.

$\frac{2 π}{| \frac{4 π}{5} |}$

Step 3.3

$\frac{4 π}{5}$ is approximately $2.51327412$ which is positive so remove the absolute value

$\frac{2 π}{\frac{4 π}{5}}$

Step 3.4

Multiply the numerator by the reciprocal of the denominator.

$2 π \frac{5}{4 π}$

Step 3.5

Cancel the common factor of $2 π$ .

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Step 3.5.1

Factor $2 π$ out of $4 π$ .

$2 π \frac{5}{2 π (2)}$

Step 3.5.2

Cancel the common factor.

$2 π \frac{5}{2 π \cdot 2}$

Step 3.5.3

Rewrite the expression.

$\frac{5}{2}$

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: $\frac{0}{\frac{4 π}{5}}$

Step 4.3

Multiply the numerator by the reciprocal of the denominator.

Phase Shift: $0 (\frac{5}{4 π})$

Step 4.4

Multiply $0$ by $\frac{5}{4 π}$ .

Phase Shift: $0$

Step 5

List the properties of the trigonometric function.

Amplitude: $\frac{7}{4}$

Period: $\frac{5}{2}$

Phase Shift: None

Vertical Shift: None

Step 6