Use the law of cosines to write an expression equivalent to b

Given:

A triangle ABC.

The given expression for b is:

To find:

The expression that is equivalent to b.

Solution:

According to the Law of Cosines,

It can be written as:

             ...(i)

We have,

                               ...(ii)

On comparing (i) and (ii), we get

Therefore, the required values are .