look familiar now?

from the unit circle, it should be clear to you that for any angle ,2. Suppose alpha and beta are central angles in the unit circle (of radius 1) with initial sides on the positive x-axis. Further suppose that alpha is in quadrant 1 and beta is in quadrant 4 such that sine of alpha is 2/3 and cosine of beta is 1/4

a) Find the exact value of cosine alpha

b) Find the exact value of sine beta