# Solving a trig equation for x

1. Nov 6, 2011

### Wessssss

1. The problem statement, all variables and given/known data
cos^2x+2sin^2x=-1

Solve for x

2. Relevant equations

3. The attempt at a solution
I don't really know how to start. I know cos^2x+sin^2x=1 but I don't think I can apply that with the 2 thrown in there.

2. Nov 6, 2011

### SteamKing

Staff Emeritus
Observe: cos^2 + 2 sin^2 = (cos^2 + sin^2) + sin^2

3. Nov 6, 2011

thank you

4. Nov 7, 2011

### HallsofIvy

Staff Emeritus
Or, if it weren't quite that obvious, you could have replaced $cos^2(x)$ with $1- sin^2(x)$. That is, [itex]cos^2(x)+ 2sin^2(x)= (1- sin^2(x))+ 2sin^2(x)= 1+ sin^2(x)= 1.