# Thread: Ran into problem with simple identity problem

1. ## Ran into problem with simple identity problem

Hi,

I have the equation 2cos^2x-sinx-1=0, and when I put 1-sin^2 in place of cos^2 I'm left with two options before factoring, either multiply by -1 to get rid of the negative in front of 2sin^2 or leave it as is. I find that if I multiply by -1, I get the correct answer of (2sin-1)(sin+1), but if I leave it negative, I get (-2sin-1)(sin-1). Is this possible, or did I make an algebra mistake?

Thanks,

Kevin

2. ## Re: Ran into problem with simple identity problem

Originally Posted by KevinShaughnessy
Hi,

I have the equation 2cos^2x-sinx-1=0, and when I put 1-sin^2 in place of cos^2 I'm left with two options before factoring, either multiply by -1 to get rid of the negative in front of 2sin^2 or leave it as is. I find that if I multiply by -1, I get the correct answer of (2sin-1)(sin+1), but if I leave it negative, I get (-2sin-1)(sin-1). Is this possible, or did I make an algebra mistake?

Thanks,

Kevin
When you made the substitution you should havobtained 2(1-sin^2(x)) -sin(x) - 1 = 0
Your error appears to be in writing (-2sin(x) -1)(sin(x) -1)