Question

A triangle has sides A, B, and C. Sides A and B are of lengths `4` and `7`, respectively, and the angle between A and B is `(2pi)/3`. What is the length of side C?

Answer 1

`C=sqrt(93)~~9.64`

Explanation:

Using the Cosine Rule:

`C^2=B^2+A^2-2BA*cos(c)`

`C^2=(7)^2+(4)^2-2(7)(4)cos((2pi)/3))`

`->C^2=49+16-(56*-1/2)=93`

`C=sqrt(93)~~9.64`