Trigonometry Examples

$y = \cos (x - \frac{3 π}{4})$

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.

$a = 1$

$b = 1$

$c = \frac{3 π}{4}$

$d = 0$

Step 2

Find the amplitude $| a |$ .

Amplitude: $1$

Step 3

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

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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 $1$ in the formula for period.

$\frac{2 π}{| 1 |}$

Step 3.3

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

$\frac{2 π}{1}$

Step 3.4

Divide $2 π$ by $1$ .

$2 π$

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: $\frac{\frac{3 π}{4}}{1}$

Step 4.3

Divide $\frac{3 π}{4}$ by $1$ .

Phase Shift: $\frac{3 π}{4}$

Step 5

List the properties of the trigonometric function.

Amplitude: $1$

Period: $2 π$

Phase Shift: $\frac{3 π}{4}$ ( $\frac{3 π}{4}$ to the right)

Vertical Shift: None

Step 6

Select a few points to graph.

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Step 6.1

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

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Step 6.1.1

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

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

Step 6.1.2

Simplify the result.

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Step 6.1.2.1

Combine the numerators over the common denominator.

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

Step 6.1.2.2

Subtract $3 π$ from $3 π$ .

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

Step 6.1.2.3

Divide $0$ by $4$ .

$f (\frac{3 π}{4}) = \cos (0)$

Step 6.1.2.4

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

$f (\frac{3 π}{4}) = 1$

Step 6.1.2.5

The final answer is $1$ .

$1$

Step 6.2

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

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Step 6.2.1

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

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

Step 6.2.2

Simplify the result.

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Step 6.2.2.1

Combine the numerators over the common denominator.

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

Step 6.2.2.2

Subtract $3 π$ from $5 π$ .

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

Step 6.2.2.3

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

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Step 6.2.2.3.1

Factor $2$ out of $2 π$ .

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

Step 6.2.2.3.2

Cancel the common factors.

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Step 6.2.2.3.2.1

Factor $2$ out of $4$ .

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

Step 6.2.2.3.2.2

Cancel the common factor.

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

Step 6.2.2.3.2.3

Rewrite the expression.

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

Step 6.2.2.4

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

$f (\frac{5 π}{4}) = 0$

Step 6.2.2.5

The final answer is $0$ .

$0$

Step 6.3

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

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Step 6.3.1

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

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

Step 6.3.2

Simplify the result.

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Step 6.3.2.1

Combine the numerators over the common denominator.

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

Step 6.3.2.2

Subtract $3 π$ from $7 π$ .

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

Step 6.3.2.3

Cancel the common factor of $4$ .

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Step 6.3.2.3.1

Cancel the common factor.

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

Step 6.3.2.3.2

Divide $π$ by $1$ .

$f (\frac{7 π}{4}) = \cos (π)$

Step 6.3.2.4

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.

$f (\frac{7 π}{4}) = - \cos (0)$

Step 6.3.2.5

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

$f (\frac{7 π}{4}) = - 1 \cdot 1$

Step 6.3.2.6

Multiply $- 1$ by $1$ .

$f (\frac{7 π}{4}) = - 1$

Step 6.3.2.7

The final answer is $- 1$ .

$- 1$

Step 6.4

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

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Step 6.4.1

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

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

Step 6.4.2

Simplify the result.

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Step 6.4.2.1

Combine the numerators over the common denominator.

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

Step 6.4.2.2

Subtract $3 π$ from $9 π$ .

$f (\frac{9 π}{4}) = \cos (\frac{6 π}{4})$

Step 6.4.2.3

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

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Step 6.4.2.3.1

Factor $2$ out of $6 π$ .

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

Step 6.4.2.3.2

Cancel the common factors.

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Step 6.4.2.3.2.1

Factor $2$ out of $4$ .

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

Step 6.4.2.3.2.2

Cancel the common factor.

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

Step 6.4.2.3.2.3

Rewrite the expression.

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

Step 6.4.2.4

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

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

Step 6.4.2.5

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

$f (\frac{9 π}{4}) = 0$

Step 6.4.2.6

The final answer is $0$ .

$0$

Step 6.5

Find the point at $x = \frac{11 π}{4}$ .

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Step 6.5.1

Replace the variable $x$ with $\frac{11 π}{4}$ in the expression.

$f (\frac{11 π}{4}) = \cos ((\frac{11 π}{4}) - \frac{3 π}{4})$

Step 6.5.2

Simplify the result.

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Step 6.5.2.1

Combine the numerators over the common denominator.

$f (\frac{11 π}{4}) = \cos (\frac{11 π - 3 π}{4})$

Step 6.5.2.2

Subtract $3 π$ from $11 π$ .

$f (\frac{11 π}{4}) = \cos (\frac{8 π}{4})$

Step 6.5.2.3

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

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Step 6.5.2.3.1

Factor $4$ out of $8 π$ .

$f (\frac{11 π}{4}) = \cos (\frac{4 (2 π)}{4})$

Step 6.5.2.3.2

Cancel the common factors.

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Step 6.5.2.3.2.1

Factor $4$ out of $4$ .

$f (\frac{11 π}{4}) = \cos (\frac{4 (2 π)}{4 (1)})$

Step 6.5.2.3.2.2

Cancel the common factor.

$f (\frac{11 π}{4}) = \cos (\frac{4 (2 π)}{4 \cdot 1})$

Step 6.5.2.3.2.3

Rewrite the expression.

$f (\frac{11 π}{4}) = \cos (\frac{2 π}{1})$

Step 6.5.2.3.2.4

Divide $2 π$ by $1$ .

$f (\frac{11 π}{4}) = \cos (2 π)$

Step 6.5.2.4

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

$f (\frac{11 π}{4}) = \cos (0)$

Step 6.5.2.5

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

$f (\frac{11 π}{4}) = 1$

Step 6.5.2.6

The final answer is $1$ .

$1$

Step 6.6

List the points in a table.

$\begin{array}{c} x & f (x) \\ \frac{3 π}{4} & 1 \\ \frac{5 π}{4} & 0 \\ \frac{7 π}{4} & - 1 \\ \frac{9 π}{4} & 0 \\ \frac{11 π}{4} & 1 \end{array}$

Step 7

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

Amplitude: $1$

Period: $2 π$

Phase Shift: $\frac{3 π}{4}$ ( $\frac{3 π}{4}$ to the right)

Vertical Shift: None

$\begin{array}{c} x & f (x) \\ \frac{3 π}{4} & 1 \\ \frac{5 π}{4} & 0 \\ \frac{7 π}{4} & - 1 \\ \frac{9 π}{4} & 0 \\ \frac{11 π}{4} & 1 \end{array}$

Step 8