Prove that $\cos^2\theta+\sin^2\theta=1$

Question

I try to find the question but I didn't

How do you do it? I'm really stuck on this proof. Can someone please explain?

What definition of cos and sin are you using? – evil999man Apr 19 '14 at 10:07 — evil999man, Apr 19 '14 at 10:07

score 2 · Answer 1 · answered Apr 19 '14 at 10:14

2

Try geometrically: draw a unitary circle and an angle $\alpha$. Then $\sin\alpha$ and $\cos\alpha$ and the radius will form exactly a right angled triangle, and the formula you're searching for will be exactly the Pitagora Theorem.

answered Apr 19 '14 at 10:14

Joe

11,745

Pythagorean* theorem? – naslundx Apr 19 '14 at 10:15
Yes. But I'm Italian and I like to call Greek men with the names I've always used (unless it gives confusion). – Joe Apr 19 '14 at 10:25
I understand. But I'm afraid very different names, such as that one, does provide confusion. – naslundx Apr 19 '14 at 10:26

Prove that $\cos^2\theta+\sin^2\theta=1$

1 Answers1