- #1

Beer w/Straw

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**The problem is... What to put as my answer :P arcsin(Sin(7Pi/5))**

**http://mathworld.wolfram.com/TrigonometryAnglesPi5.html**

**The solution is -2Pi/5**

The problem I'm having is this appears to me as a trick question. Would it be acceptable to say

sin(7pi/5) = -(sqrt(5/8+sqrt(5)/8)) make a note of an identity. Then simply say arcsin(-(sqrt(5/8+sqrt(5)/8))) =-2Pi/5?

Assuming this is correct, would not all the work I just cut out be acceptable because I'm not trying to prove the identity over again?

Comments suggestions would be appreciated.

Thanks.

PS: Sorry for lack of tex.