Question

write as product: cos(6x)+ cos2(x)

Answer 1

By the sum-to-product formula:

cos(A) + cos(B) = 2cos[(A + B)/2]cos[(A - B)/2]

With A = 6x and B = 2x:

cos(6x) + cos(2x) = 2cos[(6x + 2x)/2]cos[(6x - 2x)/2]
==> cos(6x) + cos(2x) = 2cos(4x)cos(2x).

Answer 2

cos A + cos B = 2 cos (A+B) / 2 * sos (A - B) / 2

Answer 3

\[\cos(C) + \cos(D) = 2 \cos(\frac{C + D}{2}) \cdot \cos(\frac{C - D}{2})\]

Answer 4

ohh, i forgot about that formula, thanks :)