Area is the size of the interior of a flat figure and is measured in square units.  The area formula of a triangle is similar to the area formula of a rectangle. The area of a rectangle is base times height or length times width. So how is the area of a triangle related?  Below is a triangle with legs of 5 and 6 cm.


If another triangle that is congruent to the original is flipped over and lined up on the hypotenuse of the first triangle, the shape below is created.

Triangle 2

A rectangle with a base and height of 5 cm and 6 cm, respectively. To find the area multiply 5 cm and 6 cm, producing 30 cm2.  To get the area of the blue triangle only, take half of the area of the rectangle.  The area of this triangle is 15 cm2.  Since this relationship can always be duplicated the area of a triangle is half the area of its associated rectangle. 

Formula for the area of a triangle: