Question

Prove that:
1. cos 10º – cos 50°
Sin 20°​

Answer 1

Answer:

Cos C - cos D= - 2sin(C+D)/2 sin (C-D) /2

Cos 10 - cos 50 =

- 2sin (10+50)/2 sin(10-50)/2

= - 2sin(60)/2 sin(-40)/2

= - 2sin30 sin(-20)

= - 2(1/2) (-sin20)

= - 1(-sin20)

= +sin20°=Rhs