Question

3 sin x - 4 sin³x is equal to
(9) Cos3x
(b) sin 3x
(c) Cos2x​

Answer 1

sin3x=sin(2x+x)

=sin2xcosx+cos2xsinx

=2sinxcosxcosx+(1−2sin²x)sinx

=2sinx(1−sin²x)+sinx−2sin³x

=3sinx−4sin³x