Graph y=2cos(x-pi/2)-1

$y = 2 \cos (x - \frac{π}{2}) - 1$

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

$a = 2$

$b = 1$

$c = \frac{π}{2}$

$d = - 1$

Find the amplitude $| a |$ .

Amplitude: $2$

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

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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 $1$ .

$2 π$

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

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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: $\frac{\frac{π}{2}}{1}$

Divide $\frac{π}{2}$ by $1$ .

Phase Shift: $\frac{π}{2}$

Find the vertical shift $d$ .

Vertical Shift: $- 1$

List the properties of the trigonometric function.

Amplitude: $2$

Period: $2 π$

Phase Shift: $\frac{π}{2}$ ( $\frac{π}{2}$ to the right)

Vertical Shift: $- 1$

Select a few points to graph.

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Find the point at $x = \frac{π}{2}$ .

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Replace the variable $x$ with $\frac{π}{2}$ in the expression.

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

Simplify the result.

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Simplify each term.

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Combine the numerators over the common denominator.

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

Subtract $π$ from $π$ .

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

Divide $0$ by $2$ .

$f (\frac{π}{2}) = 2 \cos (0) - 1$

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

$f (\frac{π}{2}) = 2 \cdot 1 - 1$

Multiply $2$ by $1$ .

$f (\frac{π}{2}) = 2 - 1$

Subtract $1$ from $2$ .

$f (\frac{π}{2}) = 1$

The final answer is $1$ .

$1$

Find the point at $x = π$ .

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

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

Simplify the result.

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Simplify each term.

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To write $π$ as a fraction with a common denominator, multiply by $\frac{2}{2}$ .

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

Combine $π$ and $\frac{2}{2}$ .

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

Combine the numerators over the common denominator.

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

Simplify the numerator.

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Move $2$ to the left of $π$ .

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

Subtract $π$ from $2 π$ .

$f (π) = 2 \cos (\frac{π}{2}) - 1$

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

$f (π) = 2 \cdot 0 - 1$

Multiply $2$ by $0$ .

$f (π) = 0 - 1$

Subtract $1$ from $0$ .

$f (π) = - 1$

The final answer is $- 1$ .

$- 1$

Find the point at $x = \frac{3 π}{2}$ .

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Replace the variable $x$ with $\frac{3 π}{2}$ in the expression.

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

Simplify the result.

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Simplify each term.

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Combine the numerators over the common denominator.

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

Subtract $π$ from $3 π$ .

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

Cancel the common factor of $2$ .

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Cancel the common factor.

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

Divide $π$ by $1$ .

$f (\frac{3 π}{2}) = 2 \cos (π) - 1$

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.

$f (\frac{3 π}{2}) = 2 (- \cos (0)) - 1$

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

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

Multiply $- 1$ by $1$ .

$f (\frac{3 π}{2}) = 2 \cdot - 1 - 1$

Multiply $2$ by $- 1$ .

$f (\frac{3 π}{2}) = - 2 - 1$

Subtract $1$ from $- 2$ .

$f (\frac{3 π}{2}) = - 3$

The final answer is $- 3$ .

$- 3$

Find the point at $x = 2 π$ .

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Replace the variable $x$ with $2 π$ in the expression.

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

Simplify the result.

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Simplify each term.

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To write $2 π$ as a fraction with a common denominator, multiply by $\frac{2}{2}$ .

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

Combine $2 π$ and $\frac{2}{2}$ .

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

Combine the numerators over the common denominator.

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

Simplify the numerator.

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Multiply $2$ by $2$ .

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

Subtract $π$ from $4 π$ .

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

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

$f (2 π) = 2 \cos (\frac{π}{2}) - 1$

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

$f (2 π) = 2 \cdot 0 - 1$

Multiply $2$ by $0$ .

$f (2 π) = 0 - 1$

Subtract $1$ from $0$ .

$f (2 π) = - 1$

The final answer is $- 1$ .

$- 1$

Find the point at $x = \frac{5 π}{2}$ .

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Replace the variable $x$ with $\frac{5 π}{2}$ in the expression.

$f (\frac{5 π}{2}) = 2 \cos ((\frac{5 π}{2}) - \frac{π}{2}) - 1$

Simplify the result.

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Simplify each term.

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Combine the numerators over the common denominator.

$f (\frac{5 π}{2}) = 2 \cos (\frac{5 π - π}{2}) - 1$

Subtract $π$ from $5 π$ .

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

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

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Factor $2$ out of $4 π$ .

$f (\frac{5 π}{2}) = 2 \cos (\frac{2 (2 π)}{2}) - 1$

Cancel the common factors.

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Factor $2$ out of $2$ .

$f (\frac{5 π}{2}) = 2 \cos (\frac{2 (2 π)}{2 (1)}) - 1$

Cancel the common factor.

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

Rewrite the expression.

$f (\frac{5 π}{2}) = 2 \cos (\frac{2 π}{1}) - 1$

Divide $2 π$ by $1$ .

$f (\frac{5 π}{2}) = 2 \cos (2 π) - 1$

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

$f (\frac{5 π}{2}) = 2 \cos (0) - 1$

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

$f (\frac{5 π}{2}) = 2 \cdot 1 - 1$

Multiply $2$ by $1$ .

$f (\frac{5 π}{2}) = 2 - 1$

Subtract $1$ from $2$ .

$f (\frac{5 π}{2}) = 1$

The final answer is $1$ .

$1$

List the points in a table.

$\begin{array}{c} x & f (x) \\ \frac{π}{2} & 1 \\ π & - 1 \\ \frac{3 π}{2} & - 3 \\ 2 π & - 1 \\ \frac{5 π}{2} & 1 \end{array}$

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

Amplitude: $2$

Period: $2 π$

Phase Shift: $\frac{π}{2}$ ( $\frac{π}{2}$ to the right)

Vertical Shift: $- 1$

$\begin{array}{c} x & f (x) \\ \frac{π}{2} & 1 \\ π & - 1 \\ \frac{3 π}{2} & - 3 \\ 2 π & - 1 \\ \frac{5 π}{2} & 1 \end{array}$

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