# Laws of Sine/Cosine

1. Oct 14, 2006

### manbush

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?

2. Oct 14, 2006

### arildno

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. Oct 14, 2006

### manbush

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. Oct 16, 2006