cos question

May 2010
7
0
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)
 

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Jan 2008
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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,

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

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

\(\displaystyle \cos x=-1\)

\(\displaystyle x=\{\pi\}\)
 
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May 2010
7
0
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!