Well, it helps to know it's the Pythagoras Theorem with something extra so it works for all triangles:. The side of length "8" is opposite angle C , so it is side c. The other two sides are a and b.

We just saw how to find an angle when we know three sides. It can be in either of these forms:.

The letters are different! But that doesn't matter.

## Law of Cosines, Finding Angles & Sides, SSS & SAS Triangles - Trigonometry

We can easily substitute x for a, y for b and z for c. The cosine of an obtuse angle is always negative see Unit Circle. Hide Ads About Ads.

Let's see how to use it. Example: How long is side "c" Example: What is Angle "C"? Example: Find the distance "z" The letters are different! C is the angle opposite side c.