The graph of y = sin x is the same as the graph of y = cos x shifted to the right pi/2 units. So the sine curve y = sin x is also at the same time a cosine curve: y = cos(x - pi/2).

In fact, any sine curve is also a cosine curve with a different phase shift, and any cosine curve is also a sine curve. Sine and cosine curves are collectively referred to as sinusoidal.

For the curve whose graph is shown, find at least one possible way of expressing it as a sine curve y = a sin(x - b) or as a cosine curve y = a cos(x - b). Explain why you think you have found a possible choice for a and b.