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Trigonometric functions Periodic behaviour Any function is called periodic if it “repeats” itself on intervals of any fixed length. For example the sine curve. Periodicity may be defined symbolically: A function f is periodic if there is a positive number p such that f (x+p) = f(x) for every x in the domain of f. the smallest value of p is the period of the function Periodic behaviour in nature wave motion: light, sound tides: cyclic rise and fall of seawater water waves seismic tremors Periodic functions Periodic motion Motion that repeats itself over and over is called Periodic Motion or Oscillation. It always has a stable equilibrium position 1 complete revolution 1period 1period Periodic Function Amplitude is the maximum multitude of displacement from equilibrium. It is always positive. A = max value - min value 2 Period is the the time to complete one cycle. Cycle is one complete round trip from A to -A then back to A. Periodic Function Axis of the curve is the horizontal line that is half way between the maximum and minimum values of the periodic curve. y = maximum value + minimum value 2 Periodic behaviour in physics common back-and-forth motion of a pendulum motion of a spring and a block bouncing ball circular motion Periodic behaviour in life radio waves clock mechanism repeated steps of a dancer ballet Don Quixote (32 fouette turns) music Questions: Determine the period and the amplitude of the functions Trig ratios of any angle sin = y P (x, y) cos = y 0 x y ( x 2 + y 2) x ( x 2 + y 2) x tan = y x Trig ratios of any angle sin = y (x 2 + y 2) positive cos = P (x, y) y y x 0 x tan = x ( x 2 + y 2) negative y x negative all ratios are positive only sin is positive II S A I III T C IV only tan is positive only cos is positive Special angles Special angles: 30o, 60o, 45o, 90o. Two special triangles can be used to find the exact values of the sine, cos, tan of special angles. 45o 30o 2 3 60o 1 2 1 45o 1 Radians and angle measure 1 radian is the measure of the angle subtended at the centre of a circle by arc equal to the radius of the circle r r = 1 radian a=*r r=a/ =a/r angle in radians Graph of f(x) = sin x 1 Domain : all real numbers, R. 2 Range : -1 y 1 . Graph of f(x) = cos x 1 Domain : all real numbers, R. 2 Range : -1 y 1 . Graph of f(x) = tan x 1 Domain : all real numbers, R, x /2 odd number. 2 Range : all real numbers, R . Stretches of periodic functions 2 1.5 hx = 2sinx 1 fx = sinx 0.5 sx = 0.5sinx 2 4 6 180 8 2 -0.5 360 -1 -1.5 f (x) = sin (x) -2 period = 2 = 360 amplitude = 1 -2.5 f (x) = 2 sin (x) f (x) = 0.5 sin (x) period = 2 = 360 period = 2 = 360 amplitude = 2 amplitude = 0.5 10 12 Stretches of periodic functions 4 3 2 hx = sinx 1 -2 2 -1 qx = sin2x 4 6 8 180 360 2 10 12 360 rx = sin0.5x -2 f (x) = sin (x) -3 -4 -5 period = 2 = 360 amplitude = 1 f (x) = sin (2 x) f (x) = sin (0.5 x) period = = 180 period = 4 = 720 amplitude = 1 amplitude = 1 2 Translations of periodic functions f x = sin x +b g x = sin x h x = sin x-c 4 vertical 2 -5 5 -2 horizontal -4 -6