# A Question of Definitions of Trig Functions

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• Dec 31st 2011, 10:33 AM
HallsofIvy
Re: A Question of Definitions of Trig Functions
Quote:

Originally Posted by corsica
Recall that three parameters are enough to fix the shape of a triangle. So if you know three side lengths and/or angles, then you can always find all other side lengths and angles (this is true for any triangle imaginable).

As Skeeter already pointed out, you use the Law of Sines and Law of Cosines when you're dealing with a non-right triangle.

Not exactly true. If you know only three angles, there exist an infinite number of possible side lengths.
• Dec 31st 2011, 12:07 PM
corsica
Re: A Question of Definitions of Trig Functions
Quote:

Originally Posted by HallsofIvy
Not exactly true. If you know only three angles, there exist an infinite number of possible side lengths.

You're right. Sorry, my bad. I should had said: three parameters always fix the shape of a triangle, but not necessarily its scale size.

Full overview to clear up any confusion:
• 3 side lengths known -> all angles can be calculated
• 3 angles known -> all side-ratios can be calculated, but not the absolute side lengths
• 1 angle and 2 side lengths known -> all other side lengths and angles can be calculated
• 2 angles and 1 side length known -> all other side lengths and angles can be calculated
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