Area of Triangle in Terms of Two Sides and Angle

Theorem
The area of a triangle $ABC$ is given by:
 * $\displaystyle \frac 1 2 a b \sin\theta $

where:
 * $a, b$ are two of the sides, and
 * $\theta$ is the angle between the sides (opposide the third side).

Proof

 * [[File:Triangle with angle.png]]