(First time using this code to draw diagrams)Code:b * /|\ / | \ / |h \ / | \ / | \ a*----------------*c

Lets use this triangle as an example.

h = height

Area of a triangle = 1/2 * base * height

Base = length AC

Height = length AB * sin (angle BAC)

Therefore area of triangle = 1/2 * AC * AB * sin(angle BAC)

I had to prove this when I was learning trigonometry as well.