# Math Help - cos question

1. ## cos question

Thanks

cos x + 2 cos x = -1 over the interval [0, 2 p)

2. Originally Posted by kittykat7
Thanks

cos x + 2 cos x = -1 over the interval [0, 2 p)
Hi kittykat7,

I'm going to assume that you meant to write:

$\cos^2x+2 \cos x=-1$

In which case,

$\cos^2 x+2\cos x+1=0$

$(\cos x+1)^2=0$

$\cos x=-1$

$x=\{\pi\}$

3. Originally Posted by masters
Hi kittykat7,

I'm going to assume that you meant to write:

$\cos^2x+2 \cos x=-1$

In which case,

$\cos^2 x+2\cos x+1=0$

$(\cos x+1)^2=0$

$\cos x=-1$

$x=\{\pi\}$

Thanks, I'm actually not sure what it was asking, that is how I received the question. That is one of the choices for an answer, so I am assuming that is what I was asking. Thank you for your speedy response!