Respuesta :

Finti

Answer:

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

Step-by-step 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)