Question

Plz answer fast...!!
Q.14

Answer 1

hope this is helpful

Answer 2

one method is nicely written by Rk ,,,


another you can also use like

1.} cos5π/8= cos(π/2+π/8)= -sin π/8
cos^2 (5π/8)= sin^2(π/8)

similarly

2.} cos7π/8= cos(π/2+3π/8)= - sin(3π/8)
cos^2(7π/8)= sin^2(3π/8)


so eq. becomes

cos^2((π/8) + cos^2(3π/8). + sin^2(π/8) + sin^2 (3π/8)
1+1
=2