Question

Prove that sin150 Degree * cos120 Degree + cos330 Degree * sin660 Degree = -1

Answer 1

Answer:

sin150°×cos120°+cos330°×sin660°=-1

sin(180°-30°)×cos(180°-60°)+cos(360°-30°)×sin(720°-60°)=-1

sin30°×-cos60°+cos30°×-sin60°=-1

1/2×-1/2+√3/2×-√3/2=-1

-1/4+-3/4=-1

-4/4=-1

-1=-1

HENCE PROVED