The formula for the area of any triangle equals 1/2 the base times the height. For a right triangle, this is easy to remember ,since a right triangle is half of a rectangle on one side of its diagonal, and the area of a rectangle equals base times height.Continue Reading
The base and height of a right triangle are the two sides next to the 90-degree angle. They are always smaller than the side across from the 90-degree angle, which is called the hypotenuse and is not necessary for area calculations. For example, in a right triangle with side lengths of three, four and five, five is the length of the hypotenuse, and three and four are the base and height.
Continuing with the above example, multiply three times four to get 12. This is actually the area of the rectangle that is formed by placing two exact copies of the right triangles together at the hypotenuse, which forms the diagonal of the rectangle.
Since there are two equal triangles in the rectangle, take half of the area of the rectangle to get the area of the triangle. In the example, 12 divided by two is six. Therefore, a right triangle with side lengths of three, four and five has an area of six.