Write the equation of a sine or cosine function to describe

Write the equation of a sine or cosine function to describe the graph.

amplitude = maximum point - minimum point = 1 - (-1)/2 = 2 /2 = 1

period of the graph = (3pi/4)*8 = 6pi

B = 2pi/6pi = 1/3

y = Asin(Bx - C) = sin(x/3 - C)

Point ( 9pi/4 , 1)

1 = sin(9pi/4*3 - C)

= sin(3pi/4 -C)

pi/2 = 3pi/4 - C ; C = 3pi/4 - pi/2 = (3pi -2pi)/4 = pi/4

y = sin(x/3 - pi/4)