Question

SIN3A= 3 SINA - 4sin^3A​

Answer 1

Step-by-step explanation:

sin 3A

= sin (2A + A)

= sin 2A cos A + cos 2A sin A

= 2 sin A cos A ∙ cos A + (1 - 2 sin² A) sin A

= 2 sin A (1 - sin² A) + sin A - 2 sin³ A

= 2 sin A - 2 sin³ A + sin A - 2 sin³ A

= 3 sin A - 4 sin³ A    

LHS = RHS

Therefore, sin 3A = 3 sin A - 4 sin³ A