Help with Pre-Calculus?

1) Find the angle of smallest postive measure that is coterminal with 35?/4?
The answer is 5?/4

2) Find the reference angle of 21 degrees
The answer is 21 degrees

3) Find the cos (alpha) given that sin (alpha) = 6/7 and cos (alpha) is less than 0
The answer is - square root of 13/7

I've got the answers, but I don't know how to get them. Please show work on how to solve these problems.
 
Back
Top