# Homework Help: Trigonometry question. Find the value of sinθ if cosθ=−1/4 and θ is in Quadrant II

1. Sep 20, 2012

### nukeman

1. The problem statement, all variables and given/known data

Question: Find the value of sinθ if cosθ=−1/4 and θ is in Quadrant II

I have not done TRIG in a long time. Given this question, what should I read over/review ? I don't remember how to solve these types of questions?

2. Relevant equations

3. The attempt at a solution

Not sure what kind of attempt I can do... I have to memorize the unit circle correct?

P.S. - Thanks to Mark an Sammy for recent help - Got 93% on my first of 3 midterms :)

2. Sep 20, 2012

### hotvette

Re: Trigonometry question. Find the value of sinθ if cosθ=−1/4 and θ is in Quadrant I

Might be good to draw a picture and remember the definition of cos in terms of lengths of sides of a right triangle. That should get you going in the right direction.

3. Sep 20, 2012

### LCKurtz

Re: Trigonometry question. Find the value of sinθ if cosθ=−1/4 and θ is in Quadrant I

Drawing a picture as hotvette suggests is an excellent idea. Another way is to use the fundamental identity $\sin^2\theta + \cos^2\theta = 1$ to solve for the cosine. The quadrant will help you choose the sign.