How do you use the law of cosines to find BC given a triangle ABC with Angle A=93, AC=17 and AB=28?
There are 3 forms of The Law of Cosines so we pick the appropriate one and substitute in the values. Please see below.
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:
(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