Graph y=3/2cos(x-pi/4)

$y = \frac{3}{2} \cos (x - \frac{π}{4})$

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.

$a = \frac{3}{2}$

$b = 1$

$c = \frac{π}{4}$

$d = 0$

Step 2

Find the amplitude $| a |$ .

Amplitude: $\frac{3}{2}$

Step 3

Find the period of $\frac{3 \cos (x - \frac{π}{4})}{2}$ .

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

$\frac{2 π}{| b |}$

Replace $b$ with $1$ in the formula for period.

$\frac{2 π}{| 1 |}$

The absolute value is the distance between a number and zero. The distance between $0$ and $1$ is $1$ .

$\frac{2 π}{1}$

Divide $2 π$ by $1$ .

$2 π$

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: $\frac{\frac{π}{4}}{1}$

Divide $\frac{π}{4}$ by $1$ .

Phase Shift: $\frac{π}{4}$

Step 5

List the properties of the trigonometric function.

Amplitude: $\frac{3}{2}$

Period: $2 π$

Phase Shift: $\frac{π}{4}$ ( $\frac{π}{4}$ to the right)

Vertical Shift: None

Step 6

Select a few points to graph.

Find the point at $x = \frac{π}{4}$ .

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

$f (\frac{π}{4}) = \frac{3 \cos ((\frac{π}{4}) - \frac{π}{4})}{2}$

Simplify the result.

Simplify the numerator.

Combine the numerators over the common denominator.

$f (\frac{π}{4}) = \frac{3 \cos (\frac{π - π}{4})}{2}$

Subtract $π$ from $π$ .

$f (\frac{π}{4}) = \frac{3 \cos (\frac{0}{4})}{2}$

Divide $0$ by $4$ .

$f (\frac{π}{4}) = \frac{3 \cos (0)}{2}$

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

$f (\frac{π}{4}) = \frac{3 \cdot 1}{2}$

Multiply $3$ by $1$ .

$f (\frac{π}{4}) = \frac{3}{2}$

The final answer is $\frac{3}{2}$ .

$\frac{3}{2}$

Find the point at $x = \frac{3 π}{4}$ .

Replace the variable $x$ with $\frac{3 π}{4}$ in the expression.

$f (\frac{3 π}{4}) = \frac{3 \cos ((\frac{3 π}{4}) - \frac{π}{4})}{2}$

Simplify the result.

Simplify the numerator.

Combine the numerators over the common denominator.

$f (\frac{3 π}{4}) = \frac{3 \cos (\frac{3 π - π}{4})}{2}$

Subtract $π$ from $3 π$ .

$f (\frac{3 π}{4}) = \frac{3 \cos (\frac{2 π}{4})}{2}$

Cancel the common factor of $2$ and $4$ .

Factor $2$ out of $2 π$ .

$f (\frac{3 π}{4}) = \frac{3 \cos (\frac{2 (π)}{4})}{2}$

Cancel the common factors.

Factor $2$ out of $4$ .

$f (\frac{3 π}{4}) = \frac{3 \cos (\frac{2 π}{2 \cdot 2})}{2}$

Cancel the common factor.

$f (\frac{3 π}{4}) = \frac{3 \cos (\frac{2 π}{2 \cdot 2})}{2}$

Rewrite the expression.

$f (\frac{3 π}{4}) = \frac{3 \cos (\frac{π}{2})}{2}$

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

$f (\frac{3 π}{4}) = \frac{3 \cdot 0}{2}$

Simplify the expression.

Multiply $3$ by $0$ .

$f (\frac{3 π}{4}) = \frac{0}{2}$

Divide $0$ by $2$ .

$f (\frac{3 π}{4}) = 0$

The final answer is $0$ .

$0$

Find the point at $x = \frac{5 π}{4}$ .

Replace the variable $x$ with $\frac{5 π}{4}$ in the expression.

$f (\frac{5 π}{4}) = \frac{3 \cos ((\frac{5 π}{4}) - \frac{π}{4})}{2}$

Simplify the result.

Simplify the numerator.

Combine the numerators over the common denominator.

$f (\frac{5 π}{4}) = \frac{3 \cos (\frac{5 π - π}{4})}{2}$

Subtract $π$ from $5 π$ .

$f (\frac{5 π}{4}) = \frac{3 \cos (\frac{4 π}{4})}{2}$

Cancel the common factor of $4$ .

Cancel the common factor.

$f (\frac{5 π}{4}) = \frac{3 \cos (\frac{4 π}{4})}{2}$

Divide $π$ by $1$ .

$f (\frac{5 π}{4}) = \frac{3 \cos (π)}{2}$

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.

$f (\frac{5 π}{4}) = \frac{3 (- \cos (0))}{2}$

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

$f (\frac{5 π}{4}) = \frac{3 (- 1 \cdot 1)}{2}$

Multiply $- 1$ by $1$ .

$f (\frac{5 π}{4}) = \frac{3 \cdot - 1}{2}$

Simplify the expression.

Multiply $3$ by $- 1$ .

$f (\frac{5 π}{4}) = \frac{- 3}{2}$

Move the negative in front of the fraction.

$f (\frac{5 π}{4}) = - \frac{3}{2}$

The final answer is $- \frac{3}{2}$ .

$- \frac{3}{2}$

Find the point at $x = \frac{7 π}{4}$ .

Replace the variable $x$ with $\frac{7 π}{4}$ in the expression.

$f (\frac{7 π}{4}) = \frac{3 \cos ((\frac{7 π}{4}) - \frac{π}{4})}{2}$

Simplify the result.

Simplify the numerator.

Combine the numerators over the common denominator.

$f (\frac{7 π}{4}) = \frac{3 \cos (\frac{7 π - π}{4})}{2}$

Subtract $π$ from $7 π$ .

$f (\frac{7 π}{4}) = \frac{3 \cos (\frac{6 π}{4})}{2}$

Cancel the common factor of $6$ and $4$ .

Factor $2$ out of $6 π$ .

$f (\frac{7 π}{4}) = \frac{3 \cos (\frac{2 (3 π)}{4})}{2}$

Cancel the common factors.

Factor $2$ out of $4$ .

$f (\frac{7 π}{4}) = \frac{3 \cos (\frac{2 (3 π)}{2 (2)})}{2}$

Cancel the common factor.

$f (\frac{7 π}{4}) = \frac{3 \cos (\frac{2 (3 π)}{2 \cdot 2})}{2}$

Rewrite the expression.

$f (\frac{7 π}{4}) = \frac{3 \cos (\frac{3 π}{2})}{2}$

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

$f (\frac{7 π}{4}) = \frac{3 \cos (\frac{π}{2})}{2}$

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

$f (\frac{7 π}{4}) = \frac{3 \cdot 0}{2}$

Simplify the expression.

Multiply $3$ by $0$ .

$f (\frac{7 π}{4}) = \frac{0}{2}$

Divide $0$ by $2$ .

$f (\frac{7 π}{4}) = 0$

The final answer is $0$ .

$0$

Find the point at $x = \frac{9 π}{4}$ .

Replace the variable $x$ with $\frac{9 π}{4}$ in the expression.

$f (\frac{9 π}{4}) = \frac{3 \cos ((\frac{9 π}{4}) - \frac{π}{4})}{2}$

Simplify the result.

Simplify the numerator.

Combine the numerators over the common denominator.

$f (\frac{9 π}{4}) = \frac{3 \cos (\frac{9 π - π}{4})}{2}$

Subtract $π$ from $9 π$ .

$f (\frac{9 π}{4}) = \frac{3 \cos (\frac{8 π}{4})}{2}$

Cancel the common factor of $8$ and $4$ .

Factor $4$ out of $8 π$ .

$f (\frac{9 π}{4}) = \frac{3 \cos (\frac{4 (2 π)}{4})}{2}$

Cancel the common factors.

Factor $4$ out of $4$ .

$f (\frac{9 π}{4}) = \frac{3 \cos (\frac{4 (2 π)}{4 (1)})}{2}$

Cancel the common factor.

$f (\frac{9 π}{4}) = \frac{3 \cos (\frac{4 (2 π)}{4 \cdot 1})}{2}$

Rewrite the expression.

$f (\frac{9 π}{4}) = \frac{3 \cos (\frac{2 π}{1})}{2}$

Divide $2 π$ by $1$ .

$f (\frac{9 π}{4}) = \frac{3 \cos (2 π)}{2}$

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

$f (\frac{9 π}{4}) = \frac{3 \cos (0)}{2}$

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

$f (\frac{9 π}{4}) = \frac{3 \cdot 1}{2}$

Multiply $3$ by $1$ .

$f (\frac{9 π}{4}) = \frac{3}{2}$

The final answer is $\frac{3}{2}$ .

$\frac{3}{2}$

List the points in a table.

$\begin{array}{c} x & f (x) \\ \frac{π}{4} & \frac{3}{2} \\ \frac{3 π}{4} & 0 \\ \frac{5 π}{4} & - \frac{3}{2} \\ \frac{7 π}{4} & 0 \\ \frac{9 π}{4} & \frac{3}{2} \end{array}$

Step 7

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

Amplitude: $\frac{3}{2}$

Period: $2 π$

Phase Shift: $\frac{π}{4}$ ( $\frac{π}{4}$ to the right)

Vertical Shift: None

$\begin{array}{c} x & f (x) \\ \frac{π}{4} & \frac{3}{2} \\ \frac{3 π}{4} & 0 \\ \frac{5 π}{4} & - \frac{3}{2} \\ \frac{7 π}{4} & 0 \\ \frac{9 π}{4} & \frac{3}{2} \end{array}$

Step 8

Graph y=3/2cos(x-pi/4)

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