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Graphing Sine and Cosine Functions In this lesson you will learn to graph functions of the form y = a sin bx and y = a cos bx where a and b are positive constants and x is in radian measure. The graphs of all sine and cosine functions are related to the graphs of y = sin x and y = cos x which are shown below. y = sin x y = cos x

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Graphing Sine and Cosine Functions The domain of each function is all real numbers. The range of each function is –1 y 1. Each function is periodic, which means that its graph has a repeating pattern that continues indefinitely. The maximum value of y = sin x is M = 1 and occurs when x = + 2 n π where n is any integer. The maximum value of y = cos x is also M = 1 and occurs when x = 2 n π where n is any integer. π2π2 The functions y = sin x and y = cos x have the following characteristics: The horizontal length of each cycle is called the period. The shortest repeating portion is called a cycle. The graphs of y = sin x and y = cos x each has a period of 2π.

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Graphing Sine and Cosine Functions The functions y = sin x and y = cos x have the following characteristics: The amplitude of each function’s graph is (M – m) = The minimum value of y = sin x is m = –1 and occurs when x = + 2 n π where n is any integer. The minimum value of y = cos x is also m = –1 and occurs when x = ( 2n + 1)π where n is any integer. 3π 2

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CHARACTERISTICS OF Y = A SIN BX AND Y = A COS BX Graphing Sine and Cosine Functions The amplitude and period of the graphs of y = a sin bx and y = a cos bx, where a and b are nonzero real numbers, are as follows: amplitude = |a| and period = 2π |b| The graph of y = 2 sin 4x has amplitude 2 and period =. 2π 4 π2π2 The graph of y = cos 2 π x has amplitude and period = 1. 2π Examples

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CHARACTERISTICS OF Y = A SIN BX AND Y = A COS BX Graphing Sine and Cosine Functions The amplitude and period of the graphs of y = a sin bx and y = a cos bx, where a and b are nonzero real numbers, are as follows: amplitude = |a| and period = 2π |b| The graph of y = 2 sin 4x has amplitude 2 and period =. 2π 4 π2π2 The graph of y = cos 2 π x has amplitude and period = 1. 2π Examples For a > 0 and b > 0, the graphs of y = a sin bx and y = a cos bx each have five key x -values on the interval 0 x : the x -values at which the maximum and minimum values occur and the x -intercepts. 2π b

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Graphing Sine and Cosine Functions Graph the function. y = 2 sin x SOLUTION The amplitude is a = 2 and the period is = = 2π. The five key points are: 2π b 2π 1 Intercepts: (0, 0); (2π, 0); = (π, 0) ( ) 2 , Minimum: ( ) 2 , – Maximum: ( ) 2 , ( ), 2 22 = ( ), –2 3232 =

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Graphing Sine and Cosine Functions Graph the function. SOLUTION Maximums: (0, 1) ; (π, 1) The amplitude is a = 1 and the period is = = π. The five key points are: 2π b 2π 2 y = cos 2x Intercepts: = ; =, 0 ( ) 44 , ( ) , ( ), 0 3434 Minimum: = ( ) , – ( ), –1 22

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Graphing a Cosine Function SOLUTION Graph y = cos π x The five key points are: The amplitude is a = and the period is = = π b 2π π Intercepts: = ; = ( ) 2, ( ), ( ) 2, ( ), Maximum: ; ( ) 0, 1313 ( ) 2, 1313 Minimum: = ( ) 2, – ( ) 1, 1313 –

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Graphing Sine and Cosine Functions The periodic nature of trigonometric functions is useful for modeling oscillating motions or repeating patterns that occur in real life. In such applications, the reciprocal of the period is called the frequency. Some examples are sound waves, the motion of a pendulum or a spring, and seasons of the year. The frequency gives the number of cycles per unit of time.

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Modeling with a Sine Function MUSIC When you strike a tuning fork, the vibrations cause changes in the pressure of the surrounding air. A middle-A tuning fork vibrates with frequency f = 440 hertz (cycles per second). You would strike a middle-A tuning fork with a force that produces a maximum pressure of 5 pascals. SOLUTION Write a sine model that gives the pressure P as a function of time t (in seconds). Then graph the model. In the model P = a sin b t, the maximum pressure P is 5, so a = 5. You can use the frequency to find the value of b. Frequency = 1 period 440 = b 2π 880π = b The pressure as a function of time is given by P = 5 sin 880π t.

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Modeling with a Sine Function MUSIC When you strike a tuning fork, the vibrations cause changes in the pressure of the surrounding air. A middle-A tuning fork vibrates with frequency f = 440 hertz (cycles per second). You would strike a middle-A tuning fork with a force that produces a maximum pressure of 5 pascals. The five key points are: The amplitude is a = 5 and the period is = f1f SOLUTION Write a sine model that gives the pressure P as a function of time t (in seconds). Then graph the model. Intercepts: (0, 0); ; = ( ) 1 440, 0 ( ), ( ) 1 880, 0 Maximum: = ( ), ( ) , 5 Minimum: = ( ) , –5 ( ), –

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Graphing Tangent Functions The domain is all real numbers except odd multiples of. At odd multiples of, the graph has vertical asymptotes. π2π2 π2π2 The range is all real numbers.The graph has a period of π. If a and b are nonzero real numbers, the graph of y = a tan bx has these characteristics: The period is. π| b |π| b | There are vertical asymptotes at odd multiples of. π 2| b | CHARACTERISTICS OF Y = A TAN BX The graph of y = tan x has the following characteristics. Example The graph of y = 5 tan 3x has period and asymptotes at x = (2n + 1) = + where n is any integer. π3π3 π6π6 n π3n π3 π 2(3)

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Graphing Tangent Functions The graph at the right shows five key x -values that can help you sketch the graph of y = tan x for a > 0 and b > 0. The graph of y = tan x has the following characteristics. These are the x -intercept, the x -values where the asymptotes occur, and the x -values halfway between the x -intercept and the asymptotes. At each halfway point, the function’s value is either a or – a.

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Graphing a Tangent Function SOLUTION The period is =. πbπb π4π4 Intercept: (0, 0) x =, or x = ; π8π π4π4 x = –, or x = – π8π π4π4 Halfway points: Asymptotes: Graph the function y = tan 4x. 3232, ( ) ( ) ; = 1414 π4π π , ( ) – – = – – π4π4 π ,,

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