Area of Triangle

Author:
user1917
Topic:
Area
Move point C (in Red) to have a triangle of greater/smaller height. Move point D (in Blue) to have a triangle of greater/smaller width. Move point G to change the shape of the triangle.
What can you say about how the area of the triangle is related to the area of the rectangle? Write down a formula for the area of the triangle in terms of the length and the width of the rectangle.