Question

If A =30^o, then prove that :
sin 3A = 3 sin A - 4 sin³A.

Answer 1

Given A = 30°

sin 3A = sin 3(30°)
= sin 90°
=1

3 sin A – 4 sin³A = 3 sin 30° – 4 sin³30°

=`3(1/2) – 4(1/2)^3`

= `(3)/(2) – (1)/(2)`

= 1

∴ sin 3A = 3 sin A – 4 sin³A