Need help with finding the value of expressions.

1.  remember   cos^2 + sin^2 = 1

            sin^2 = 1- cos^2

             sin = sqrt (15/16)       (we are only concerned about the POSITIVE root in the 1st quadrant)

tan = sin/cos       sqrt(15/16) / 1/4   = 4 sqrt(15/16)   = 3.873

2.  sin (theta - pi/2)    results in shifting the sin wave pi/2 to the right which is an inverted cos wave

       so sin (theta-pi/2)    is   - cos(theta) =  - .54