Question

Question #61f5a

Answer 1

Use the sum-to-product formula for cosine

Explanation:

The sum-to-product formula for cosine states:

`cos(A) + cos(B) = 2cos((A+B)/2)cos((A-B)/2)`

Specifically, that gives

`cos(5x) + cos(3x) = cos(4x)cos(x)`

Therefore the equation is equivalent to

`cos(4x)cos(x) = cos(x)`

This equation has solutions when cosx = 0 or when

cos(4x) = 1.

Solve these much simpler equations, and you're done.