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.