Question

Prove: cos(3θ)=sin(2θ)

Answer 1

Explanation:

By taking ( θ = 18°)

L.H.S

cos(3θ)=sin(2θ)

cos(3θ)= cos( 3X18°)= cos (54°)

= cos[
`(\pi )/(2)` - (2x18°)] ∵[
`(\pi )/(2)` - (2x18°) = 54°]

= ∴ sin ( 2x18°)

As θ = 18°

= sin (2θ) = R.H.S