# Thread: Having trouble solving 4*(1+ sin theta) = cos^2 theta

1. ## Having trouble solving 4*(1+ sin theta) = cos^2 theta

Hello all!

Could someone please explain to me how to get started solving this equation? 4*(1+ sin theta) = cos^2 theta
I am really at a loss.

Thank you thank you!
~Nikki

2. ## Re: Having trouble solving 4*(1+ sin theta) = cos^2 theta

If you replace $\cos^2\theta$ with $1-\sin^2\theta$, then you'll get a quadratic equation in $\sin\theta$.

3. ## Re: Having trouble solving 4*(1+ sin theta) = cos^2 theta

Originally Posted by ansulli2
Hello all!

Could someone please explain to me how to get started solving this equation? 4*(1+ sin theta) = cos^2 theta
I am really at a loss.

Thank you thank you!
~Nikki
WA , click "show steps"

4. ## Re: Having trouble solving 4*(1+ sin theta) = cos^2 theta

Thank you thank you! So I worked through the problem and I got two solutions -1 and -3, which means on the unit circle only -1 is a correct solution. Right?

~Nikki

5. ## Re: Having trouble solving 4*(1+ sin theta) = cos^2 theta

Originally Posted by ansulli2
So I worked through the problem and I got two solutions -1 and -3, which means on the unit circle only -1 is a correct solution. Right?
Yes, and then you need to solve $\sin\theta=-1$.

6. ## Re: Having trouble solving 4*(1+ sin theta) = cos^2 theta

Originally Posted by ansulli2
Thank you thank you! So I worked through the problem and I got two solutions -1 and -3, which means on the unit circle only -1 is a correct solution. Right?

~Nikki
$\sin{\theta} = -1$

remember you're solving for $\theta$ ...

7. ## Re: Having trouble solving 4*(1+ sin theta) = cos^2 theta

Thanks all of you, that really helped and now I can work on the rest of the HW problems with a LOT less confusion ^_^

~Nikki