Question

Find the exact value of the trig expression given that sin u = -5/13 and cos v = -4/5.

u and v are in the second quadrant.

cos(v - u)

Answer 1

well, just remember that

sin = y/r
cos = x/r

sin u cannot be negative if u is in QII.

Anyway, just recall your common triangles: 5-12-13 and 3-4-5. Draw them in the proper quadrant and find the missing side.

Then just plug the numbers into your difference formula for cosine.

Answer 2

Thanks Steve