Question

Which expression is equivalent to cos(4x)+cos(2x)

Answer 1

2*cos(3x)*cos(x)

Explanation:

cos(4x) + cos(2x)

=cos(3x+x) + cos(3x-x)

Formula: cosx cosy=1/2(cos(x+y)+cos(x-y))

Here, x will be 3x according to formula and y will be equal to x

So, cos(3x+x) + cos(3x-x)

=2*cos(3x)*cos(x)