# How do you use the law of cosines to find BC given a triangle ABC with Angle A=93, AC=17 and AB=28?

##### 2 Answers

There are 3 forms of The Law of Cosines so we pick the appropriate one and substitute in the values. Please see below.

#### Explanation:

Let's change the notation to be where angles are in uppercase and the side opposite that is the same letter but in lowercase:

Side AC becomes side

Side AB becomes side

Side BC becomes side

Also unknown are

The one of the three forms of the Law of Cosines that we need is:

Substitute in the known values

solve for a:

#### Explanation:

Given

(I've assumed the "degree" part)

and using the standard convention lettering

The Law of Cosines tells us that

In this case

using a calculator

and