Laws of Sine/Cosine

  • Thread starter manbush
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  • #1
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Main Question or Discussion Point

Law of Sine = Sin A/a = Sin B /b = Sin c/c

Law of Cosines
a^2=b^2 + c^2 - 2bc Cos A

I used to know how to "prove" both of these laws but I haven't touched math for years.

Can someone "prove" them or "explain" what these laws exactly mean?
 

Answers and Replies

  • #2
arildno
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As for the law of sines:
Use the sine law for the AREA of triangles in a clever way!

As for the cosine law:
Make a triangle with acute angles, draw its height h, so that you have two right-angled triangles.
Fiddle around with the Pythogorean theorem until you stumble upon the law of cosine
 
  • #3
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Sorry, I don't understand either. I been away from math too long. I know I could just use these formulas but I want to see the "proof".

Is it possible you could show me an example of proving them?
 
  • #4
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My friend taught me this...dont' quite remember, i would appreciate any help :D
 

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