1. cos question

Please help me solve this problem.... it's been awhile so I am a bit rusty!
Thanks

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

2. Originally Posted by kittykat7
Please help me solve this problem.... it's been awhile so I am a bit rusty!
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:

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

In which case,

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

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

$\displaystyle \cos x=-1$

$\displaystyle x=\{\pi\}$

3. Originally Posted by masters
Hi kittykat7,

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

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

In which case,

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

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

$\displaystyle \cos x=-1$

$\displaystyle x=\{\pi\}$

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!