hi, amm, why cos^2a+cos^2b+ cos^2 c =1 ? i have to explain it in class :/

Question

hero · Answer

I wonder what the a, b, and c represent.

anonymous · Answer

angles

hero · Answer

I know that, but what is the relationship between angles a, b, and c?

anonymous · Answer

oh! i really don't know , we are learning about vectors in 3d, and the teacher gave us that homework :/

hero · Answer

Hmm, I found this identity here: http://en.wikibooks.org/wiki/Trigonometry/For_Enthusiasts/Less-Used_Trig_Identities

anonymous · Answer

thank you!

anonymous · Answer

but is isnt true
assuming that $a, b, c$ are the internal angles of a triangle, take for example $a=b=c=\frac{\pi}{3}$

hero · Answer

That's why I linked the link @satellite73

anonymous · Answer

then $\cos(\frac{\pi}{3})=\frac{1}{2}$ and it is not true that 
$$3\times\frac{1}{2}=1$$

anonymous · Answer

ahh so i see

anonymous · Answer

o.0 im new in this level of math U.U so i don't really know to much about this U.U

goformit100 · Answer

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