∫−ππ (cos⁡px−sin⁡qx)2dx where p and q are in tegers is equal to

I=∫−ππ cos2⁡px+sin2⁡qx−2cos⁡pxsin⁡qxdx=∫0π [2+cos⁡2px−cos⁡2qx]dx=2π[∵third term in the integrand is odd]