Evaluate the trigonometric function by using the quadrant and the reference angle to determine the sign and absolute value. Round your answer to the nearest thousandth. cos 25π/4

Answer 1

A complete rotation is 2pi which is 8p/4 so you have 3 complete rotations plus pi/4 so reference angle is pi/4 which is in quadrant 1 where cosine is positive

Cosine pi/4 = sqroot2/2