"If tan(theta) = 1/2, find sin(theta) using trig identities."

I know how to do this with triangles: use pyth. thm to find the hypotenuse, and read off the answer. But what identity should I use?

"If tan(theta) = 1/2, find sin(theta) using trig identities."

I know how to do this with triangles: use pyth. thm to find the hypotenuse, and read off the answer. But what identity should I use?

I know how to do this with triangles: use pyth. thm to find the hypotenuse, and read off the answer. But what identity should I use?

- little_dragon
**Posts:**221**Joined:**Mon Dec 08, 2008 5:18 pm-
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I don't know identities but I've learned sin^2(@)+cos^2(@)=1. Try doing the tagent with sines and cosines.

tan(@) = 1/2 = sin(@)/cos(@)

Square both sides, and multiply acorss to get cos^2(@) = 4sin^2(@). Then add a sine to both sides to get cos^2(@)+sin^2(@)=5sin^2(@)=1. Then sin^2(@)=1/5. Do the square roots to get the answer.

tan(@) = 1/2 = sin(@)/cos(@)

Square both sides, and multiply acorss to get cos^2(@) = 4sin^2(@). Then add a sine to both sides to get cos^2(@)+sin^2(@)=5sin^2(@)=1. Then sin^2(@)=1/5. Do the square roots to get the answer.

I don't know what identities you have? The way the other post gave might be as good as any. But if you have to use something else, you could do 1 + tan^{2}(theta) = sec^{2}(theta) = 1/cos^{2}(theta) = 1/{1 - sin^{2}(theta)}, and plug in that 1 + tan^{2}(theta) = 5/4. The answer works out the same.