Question

Determine whether the equation is an identity.

cos(3 theta) = 4(cos(theta))^3 - 3 cos(theta)

Answer 1

i did this earlier on

Answer 2

use cos(A+B) = cosAcosB - sinAsinB
sin(A+B) = sinAcosB + sinBcosA
and expand cos(3 theta)
u will get the RHS expression