SOLUTION: find the exact value, leaving the answer in a proper form of cos 135 degrees.

Algebra ->  Trigonometry-basics -> SOLUTION: find the exact value, leaving the answer in a proper form of cos 135 degrees.      Log On


   

Question 33124: find the exact value, leaving the answer in a proper form of cos 135 degrees.
Answer by sarah_adam(201) About Me  (Show Source):
You can put this solution on YOUR website!
Cos (135)
Cos(90+45)
Cos(A+B) = cos A cos B - sin A sin B
Cos(90+45) = cos 90 cos 45 - sin 90 sin 45
cos 90 = 0 , cos 45 = (1/sqrt%282%29) , sin 90 = 1,
sin 45 = (1/sqrt%282%29)
Substituting the calues
cos(135) = 0 - 1* (1/sqrt%282%29)
Cos (135)= - (1/sqrt%282%29)