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#1 2005-10-31 06:10:43
- Lloyd W
- Guest
Trigonometry help
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
#2 2005-10-31 06:42:01
- mathsyperson
- Moderator
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Re: Trigonometry help
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.