A triangle has sides A, B, and C. Sides A and B are of lengths #1# and #7#, respectively, and the angle between A and B is #(2pi)/3 #. What is the length of side C?
First of all let me denote the sides with small letters
Let me name the angle between side "a" and "b" by
Note:- the sign
We are given with
It is given that
Using Law of Cosines