Write down the triangle area formula -- A = 1/2 * b * h -- on a piece of paper. "A" stands for area, "b" for the base length and "h" for height. The height is the perpendicular distance from the apex, or top of the triangle, to the base.
Use the information in a given math problem to find the area of a triangle. For example, suppose that the base is 10 inches and the height is 7 inches.
Plug the numbers into the formula: A = 1/2 * 10 *7.
Do the multiplication: 1/2 x 10 = 5, and 5 x 7 = 35. Concluding the example, the area of the triangle would be 35 square inches.