# Thread: Area of a Triangle.

1. ## Area of a Triangle.

https://8842006143235788137-a-180274...attredirects=0

I don't know where to start. Some of my friends told me that I need an Angle!
Any advice?

2. ## Re: Area of a Triangle.

Originally Posted by kreshnik
https://8842006143235788137-a-180274...attredirects=0

I don't know where to start. Some of my friends told me that I need an Angle!
Any advice?
You can use the cos rule on triangle ABC to find angle B

$\displaystyle \cos(B) = \frac{|AB|^2+|BC|^2 - |AC|^2}{2|AB||BC|}$

3. ## Re: Area of a Triangle.

It's also possible to find the area of ABC using Heron's formula, and from there easily find the area of ACD.