Definition: The area of a triangle equals one half times its base times its height, A = (1/2)bh, measured in square units.
What is the formula?
A = (1/2) x b x h, where b is the base and h is the height measured perpendicular to that base.
Why one half?
Two identical triangles form a parallelogram with area bh. Each triangle is half of it.
How do you use it?
A triangular sail has base 14 feet and height 9 feet.
- Multiply: 14 x 9 = 126.
- Halve it: 126 / 2 = 63.
The area is 63 square feet.
How does it help with other shapes?
Decompose polygons into triangles and rectangles, find each area, and add. A trapezoid with parallel sides 5 and 11 and height 4 splits into two triangles of areas (1/2)(5)(4) = 10 and (1/2)(11)(4) = 22, for a total of 32.
What is the typical error?
Using a slanted side as the height. The height is the perpendicular distance from the base to the opposite vertex, which might fall outside the triangle in an obtuse case. Also, do not forget the one half.