Question

prove problem cos3x = 4 cot^3x - 3 cot x first pu ncert textbook​

Answer 1

Answer:

Apply the trig identities:

cos2x

=2cos2x-1sin2x

=2sinx⋅cosx

We get:

cos3x

=cos(x+2x)

=cosx⋅cos2x−sinx⋅sin2x

=cosx(2cos2x−1)−2sin2x⋅cosx

=2cos3x−cosx−2cosx(1−cos2x)

=2cos3x−cosx−2cosx+2cos3x

So,cos3x=4cos3x−3cosx