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**Lloyd W****Guest**

Hi there, I am studying Trig at the moment and am a bit confused by this question i have been asked:

Using the definitions of Sine and Cosine in a righthanded triangle calculate the value of sin² +cos² . Use pythagoras theorem to help you.

ok, so adj² +opp² = hyp²

and sin+tanxcos and cos=sin/tan

i guess im supposed to use that. but what exactly is this VALUE im supposed to be finding.

I am so confused, please advise me.

- Lloyd

**mathsyperson****Moderator**- Registered: 2005-06-22
- Posts: 4,900

You're on the right lines. cos = adj/hyp and sin = opp/hyp, so cos² = adj²/hyp² and sin² = opp²/hyp². So cos² + sin ² = (adj² + opp²)/hyp².

But Pythagoras's Theorem says that a² + b² = c², where c is the hypotenuse, so that means that adj² + opp² = hyp². Therefore, cos² + sin² = hyp²/hyp² = 1.

That's an identity that you'll be using a lot while you're studying trig, so remember it well.

Why did the vector cross the road?

It wanted to be normal.

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**Lloyd W****Guest**

wicked, i should have figured that out. cheers

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