A and B are complementary angles. So, A + B = 90 ; A = 90 – B sin A = sin (90 – B) = cos B cos A = cos (90 – B) = sin B tan A = tan (90 – B) = cot B cot A = cot (90 – B) = tan B Given, sin A cos B + cos A sin B – tan A t an B +sec2A–cot2B =sin2 A + cos2 B – cot B tan B + sec2 A – tan2 A = 1 – 1 + 1 = 1