# Simple trig question

1. May 5, 2014

### cosmictide

Hi guys,

This has caused me some confusion. Any help in this regard would be greatly appreciated.
1. The problem statement, all variables and given/known data

Given that $\theta$ is an acute angle with sin$\theta$=19/51 find the exact value of cos$\theta$

2. Relevant equations

3. The attempt at a solution

All I seem to be getting based on my calculations are approximations. I have no idea how to actually obtain the exact value. Initially I took the inverse of sin$\theta$ to get $\theta$=21.872....degree. Therefore the cos$\theta$=0.928....I also tried using a right-angled triangle and finding the adjacent which I calculated to be 47.328... and dividing adj by hyp to see whether I get an exact value but got the same answer as before.

Any help in this regard would be greatly appreciated.

2. May 5, 2014

### BvU

What about $\sin^2 + \cos^2 = 1$, exactly ? It means you get a square root in your answer, but it definitely is exact.

3. May 5, 2014

### cosmictide

:rofl: Genius.

Thank you so much, I can't believe I didn't think of that.