How to factor cos22X + cos2X = 0

[Aceradonia]

How do I factor this?

cos²2X + cos2X = 0

 

[tiny-tim]

Welcome to PF!

Hi Aceradonia ! Welcome to PF!

How do I factor this?

cos²2X + cos2X = 0

Well, cos²2X is the same as (cos2X)²,

so you can factor out a cos2X.

hmm … did you mean solve, rather than factor? … then cos2x = 0 is one set of solutions, and the other is … ?

 

[Дьявол]

You will easy realize it, maybe (not necessarily) if you substitute for cos2X=y, you will come up with y²+y=0. Out of there: y(y+1)=0