Insanely easy question - trig functions, need a quick question answered

[andrew.c]

Homework Statement

I need to solve the equation $$cos 5x + cos 3x = cos x$$

Do the first two terms add together to be cos 8x? Then use double angle formula to solve?

 

[rl.bhat]

Homework Statement

I need to solve the equation $$cos 5x + cos 3x = cos x$$

Do the first two terms add together to be cos 8x? Then use double angle formula to solve?

No. cos 5x + cos 3x is not equal to cos8x.
Use formula to convert sum of trig. function to product form.