find the exact value cos (-5 pi/ 12)

Answer 1

( - 5 pi / 12 ) rad = - 75 °

cos ( - x ) = cos x

cos ( - 5 pi / 12 ) rad = cos ( 75 ° )

75 ° = 45 ° + 30 °

cos ( A + B ) = cos ( A ) * cos ( B ) - sin ( A ) * Sin ( B )

cos ( 75 ° ) = cos ( 45 ° + 30 ° ) = cos ( 45° ) * cos ( 30 ° ) - sin ( 45 ° ) * sin ( 30 ° )

Calculate this.

Exact value :

cos ( - 5 pi / 12 ) = ( sqrt 3 - 1 ) / ( 2 * sqrt 2 )

Answer 2

Suppose sin x =4/5 , 0<x<pi/2 and cos y = -1/2, pi/2 <y< pi

evaluate
cos (x-y)