tunjukan bahwa 2 sin (45-x) sin (135-x) = 1 + sin 2x

2 sin (45 - x)  sin (135 - x ) = 1 + sin 2x

- { -2 sin (45-x) sin(135-x)} =
= - {cos(45-x+135 -x) .- cos (45-x -135 + x)}
= - { cos (180 - 2x) - cos (-90)}
= - { - cos 2x - 0)
= cos 2x
= 1 - 2 sin² x