Question

find the exact value of the given expression Cos(60*+315*)

Answer 1

it should be the same value as cos(15)

Answer 2

cos (60+315) = cos(375)= cos(360+15)

Answer 3

cos (15) = cos(45-30)

Answer 4

use the formula cos (a-b)= cos a cos b - sin a sin b

Answer 5

therefore, cos (15) = cos 45 cos 30 - sin 45 sin 30