Question

In triangle ABC, a = 9, c = 5, and B = 120°. Find b^2

Answer 1

We can find b by using the cosine rule of a triangle.

$b^2=a^2+c^2-2ac CosB$

First step is to plug in the given values in the above equation. So,

$b^2=9^2+5^2-2*9*5*Cos (120)$

$b^2=81+25-90(-\frac{1}{2} )$

=106+45

=151

So, b^2=151