SOLUTION: Find the exact value of cos(-9π/4). Put answer in exact form. I tried converting to degrees but I got stuck.

Algebra ->  Trigonometry-basics -> SOLUTION: Find the exact value of cos(-9π/4). Put answer in exact form. I tried converting to degrees but I got stuck.       Log On


   

Question 863381: Find the exact value of cos(-9π/4). Put answer in exact form.
I tried converting to degrees but I got stuck.
Answer by Alan3354(69443) About Me  (Show Source):
You can put this solution on YOUR website!
cos(-9pi/4)
Add 2pi
= cos(-pi/4) = cos(pi/4)
= sqrt%282%29%2F2