Question

prove that sin²40°- cos²50°=0

Answer 1

${ \sin }^{2} 40 - { \cos}^{2} 50 \\ = { \sin }^{2} 40 - { \sin}^{2} (90 - 50 ) \\ = { \sin }^{2} 40 - { \sin }^{2} 40 = 0$

Answer 2

Cos 50 = sin 40
Hence proved