Question

find the equation of the cosine function ith an amplitude of 2/3, 3 pi, phase shift of -2 pi, and vertical shift of 1/3 units down

Answer 1

first you should look at the general cosine wave:\[y(x)=A \cos(bx+c)+K\]
Since the cosine wave reaches a maximum of 1, when you multiply it by A it is now the higher distance from the simetry axis, so A is the amplitude.