Question

Find the exact value of cos 315°.

Answer 1

315 degrees is 45 degrees away from 0 degrees.
Therefore sin(315)=cos(315).
You also know that for any angle, x,
sin%5E2%28x%29%2Bcos%5E2%28x%29=1
In this case,

cos%5E2%28315%29%2Bcos%5E2%28315%29=1
2cos%5E2%28315%29=1
cos%5E2%28315%29=1%2F2
cos%28315%29=1%2Fsqrt%282%29
cos%28315%29=sqrt%282%29%2F2

Answer 2

Crap the numbers dont work D:

Answer 3

\[\frac{ \sqrt{2} }{ 2 }\] its C