Deriving the Formulas for the Area of a Triangle
How are these equations derived?
Look at: 
.
This equation is used when you are given two sides and an included angle (SAS).
Look at the following triangle:
K = Area of the triangle
Solving for h:
Substitute the value found for h into 
:
If you redraw the altitudes, or heights, you can develop two different formulas as listed previously.