₀ഽπ/4 = _ 1 ₀ഽ cos (5x + x) – cos (5x – x) dx
2
= _ 1 ₀ഽ (cos6x – cos4x)dx
2
= _ 1 [ 1sin6x – 1sin4x ]π/4
2 6 4 0
= [ _ 1 sin6x + 1 sin4x]π/4
12 8 0
= [ _ 1 sin3π + 1 sinπ)-( _ 1 sin0 + 1 sin0)
12 8 12 8
= _ 1 (-1) + 1 (0) – 0
12 8
= 1
12