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For the equation A cos ( B x + C ) + D , what constants affect the range of the function and how do they affect the range?

The absolute value of the constant A (amplitude) increases the total range and the constant D (vertical shift) shifts the graph vertically.

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How does the range of a translated sine function relate to the equation y = A sin ( B x + C ) + D ?

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How can the unit circle be used to construct the graph of f ( t ) = sin t ?

At the point where the terminal side of t intersects the unit circle, you can determine that the sin t equals the y -coordinate of the point.

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Graphical

For the following exercises, graph two full periods of each function and state the amplitude, period, and midline. State the maximum and minimum y -values and their corresponding x -values on one period for x > 0. Round answers to two decimal places if necessary.

f ( x ) = 2 3 cos x

A graph of (2/3)cos(x). Graph has amplitude of 2/3, period of 2pi, and range of [-2/3, 2/3].

amplitude: 2 3 ; period: 2 π ; midline: y = 0 ; maximum: y = 2 3 occurs at x = 0 ; minimum: y = 2 3 occurs at x = π ; for one period, the graph starts at 0 and ends at 2 π

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f ( x ) = 3 sin x

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f ( x ) = 4 sin x

A graph of 4sin(x). Graph has amplitude of 4, period of 2pi, and range of [-4, 4].

amplitude: 4; period: 2 π ; midline: y = 0 ; maximum y = 4 occurs at x = π 2 ; minimum: y = 4 occurs at x = 3 π 2 ; one full period occurs from x = 0 to x = 2 π

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f ( x ) = cos ( 2 x )

A graph of cos(2x). Graph has amplitude of 1, period of pi, and range of [-1,1].

amplitude: 1; period: π ; midline: y = 0 ; maximum: y = 1 occurs at x = π ; minimum: y = 1 occurs at x = π 2 ; one full period is graphed from x = 0 to x = π

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f ( x ) = 2 sin ( 1 2 x )

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f ( x ) = 4 cos ( π x )

A graph of 4cos(pi*x). Grpah has amplitude of 4, period of 2, and range of [-4, 4].

amplitude: 4; period: 2; midline: y = 0 ; maximum: y = 4 occurs at x = 0 ; minimum: y = 4 occurs at x = 1

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f ( x ) = 3 cos ( 6 5 x )

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y = 3 sin ( 8 ( x + 4 ) ) + 5

A graph of 3sin(8(x+4))+5. Graph has amplitude of 3, range of [2, 8], and period of pi/4.

amplitude: 3; period: π 4 ; midline: y = 5 ; maximum: y = 8 occurs at x = 0.12 ; minimum: y = 2 occurs at x = 0.516 ; horizontal shift: 4 ; vertical translation 5; one period occurs from x = 0 to x = π 4

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y = 2 sin ( 3 x 21 ) + 4

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y = 5 sin ( 5 x + 20 ) 2

A graph of 5sin(5x+20)-2. Graph has an amplitude of 5, period of 2pi/5, and range of [-7,3].

amplitude: 5; period: 2 π 5 ; midline: y = −2 ; maximum: y = 3 occurs at x = 0.08 ; minimum: y = −7 occurs at x = 0.71; phase shift: −4 ; vertical translation: −2; one full period can be graphed on x = 0 to x = 2 π 5

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For the following exercises, graph one full period of each function, starting at x = 0. For each function, state the amplitude, period, and midline. State the maximum and minimum y -values and their corresponding x -values on one period for x > 0. State the phase shift and vertical translation, if applicable. Round answers to two decimal places if necessary.

f ( t ) = 2 sin ( t 5 π 6 )

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f ( t ) = cos ( t + π 3 ) + 1

A graph of -cos(t+pi/3)+1. Graph has amplitude of 1, period of 2pi, and range of [0,2]. Phase shifted pi/3 to the left.

amplitude: 1 ; period: 2 π ; midline: y = 1 ; maximum: y = 2 occurs at x = 2.09 ; maximum: y = 2 occurs at t = 2.09 ; minimum: y = 0 occurs at t = 5.24 ; phase shift: π 3 ; vertical translation: 1; one full period is from t = 0 to t = 2 π

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f ( t ) = 4 cos ( 2 ( t + π 4 ) ) 3

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f ( t ) = sin ( 1 2 t + 5 π 3 )

A graph of -sin((1/2)*t + 5pi/3). Graph has amplitude of 1, range of [-1,1], period of 4pi, and a phase shift of -10pi/3.

amplitude: 1; period: 4 π ; midline: y = 0 ; maximum: y = 1 occurs at t = 11.52 ; minimum: y = 1 occurs at t = 5.24 ; phase shift: 10 π 3 ; vertical shift: 0

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f ( x ) = 4 sin ( π 2 ( x 3 ) ) + 7

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Determine the amplitude, midline, period, and an equation involving the sine function for the graph shown in [link] .

A sinusoidal graph with amplitude of 2, range of [-5, -1], period of 4, and midline at y=-3.

amplitude: 2; midline: y = 3 ; period: 4; equation: f ( x ) = 2 sin ( π 2 x ) 3

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Determine the amplitude, period, midline, and an equation involving cosine for the graph shown in [link] .

A graph with a cosine parent function, with amplitude of 3, period of pi, midline at y=-1, and range of [-4,2]
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Determine the amplitude, period, midline, and an equation involving cosine for the graph shown in [link] .

A graph with a cosine parent function with an amplitude of 2, period of 5, midline at y=3, and a range of [1,5].

amplitude: 2; period: 5; midline: y = 3 ; equation: f ( x ) = 2 cos ( 2 π 5 x ) + 3

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Determine the amplitude, period, midline, and an equation involving sine for the graph shown in [link] .

A sinusoidal graph with amplitude of 4, period of 10, midline at y=0, and range [-4,4].
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Determine the amplitude, period, midline, and an equation involving cosine for the graph shown in [link] .

A graph with cosine parent function, range of function is [-4,4], amplitude of 4, period of 2.

amplitude: 4; period: 2; midline: y = 0 ; equation: f ( x ) = 4 cos ( π ( x π 2 ) )

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Determine the amplitude, period, midline, and an equation involving sine for the graph shown in [link] .

A graph with sine parent function. Amplitude 2, period 2, midline y=0
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Determine the amplitude, period, midline, and an equation involving cosine for the graph shown in [link] .

A graph with cosine parent function. Amplitude 2, period 2, midline y=1

amplitude: 2; period: 2; midline y = 1 ; equation: f ( x ) = 2 cos ( π x ) + 1

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Determine the amplitude, period, midline, and an equation involving sine for the graph shown in [link] .

A graph with a sine parent function. Amplitude 1, period 4 and midline y=0.
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Algebraic

For the following exercises, let f ( x ) = sin x .

On [ 0 , 2 π ), solve f ( x ) = 0.

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On [ 0 , 2 π ), solve f ( x ) = 1 2 .

π 6 , 5 π 6

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Evaluate f ( π 2 ) .

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On [ 0 , 2 π ) , f ( x ) = 2 2 . Find all values of x .

π 4 , 3 π 4

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On [ 0 , 2 π ), the maximum value(s) of the function occur(s) at what x -value(s)?

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On [ 0 , 2 π ), the minimum value(s) of the function occur(s) at what x -value(s)?

3 π 2

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Show that f ( x ) = f ( x ) . This means that f ( x ) = sin x is an odd function and possesses symmetry with respect to ________________.

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For the following exercises, let f ( x ) = cos x .

On [ 0 , 2 π ), solve the equation f ( x ) = cos x = 0.

π 2 , 3 π 2

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On [ 0 , 2 π ), solve f ( x ) = 1 2 .

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On [ 0 , 2 π ), find the x -intercepts of f ( x ) = cos x .

π 2 , 3 π 2

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On [ 0 , 2 π ), find the x -values at which the function has a maximum or minimum value.

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On [ 0 , 2 π ), solve the equation f ( x ) = 3 2 .

π 6 , 11 π 6

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Technology

Graph h ( x ) = x + sin x on [ 0 , 2 π ] . Explain why the graph appears as it does.

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Graph h ( x ) = x + sin x on [ 100 , 100 ] . Did the graph appear as predicted in the previous exercise?

The graph appears linear. The linear functions dominate the shape of the graph for large values of x .

A sinusoidal graph that increases like the function y=x, shown from 0 to 100.
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Graph f ( x ) = x sin x on [ 0 , 2 π ] and verbalize how the graph varies from the graph of f ( x ) = sin x .

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Graph f ( x ) = x sin x on the window [ −10 , 10 ] and explain what the graph shows.

The graph is symmetric with respect to the y -axis and there is no amplitude because the function is not periodic.

A sinusoidal graph that has increasing peaks and decreasing lows as the absolute value of x increases.
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Graph f ( x ) = sin x x on the window [ −5 π , 5 π ] and explain what the graph shows.

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Real-world applications

A Ferris wheel is 25 meters in diameter and boarded from a platform that is 1 meter above the ground. The six o’clock position on the Ferris wheel is level with the loading platform. The wheel completes 1 full revolution in 10 minutes. The function h ( t ) gives a person’s height in meters above the ground t minutes after the wheel begins to turn.

  1. Find the amplitude, midline, and period of h ( t ) .
  2. Find a formula for the height function h ( t ) .
  3. How high off the ground is a person after 5 minutes?
  1. Amplitude: 12.5; period: 10; midline: y = 13.5 ;
  2. h ( t ) = 12.5 sin ( π 5 ( t 2.5 ) ) + 13.5 ;
  3. 26 ft
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Practice Key Terms 5

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Source:  OpenStax, Precalculus. OpenStax CNX. Jan 19, 2016 Download for free at https://legacy.cnx.org/content/col11667/1.6
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