Find the exact value of cos 165 degrees. Use square root (x)to express the radical of x.

Question

Find the exact value of cos 165 degrees. Use square root (x) to express the radical x.

Answer 1

cos165° = cos(120°+45°)

 

            = cos120°cos45° - sin120°sin45°

 

            = (-1/2)(√2/2) - (√3/2)(√2/2) = (-√2-√6)/4

Answer 2

 Deleting previous answer