A special right triangle is a right triangle with some regular feature that makes calculations on the triangle easier, or for which simple formulas exist. For example, a right triangle may have angles that form a simple ratio, such as 45-45-90. This is called an "angle based" right triangle. A "side based" right triangle is one in which the lengths of the sides form a whole number ratio, such as 3-4-5. Knowing the ratios of the angles kjjkjor sides of these special right triangles allows one to quickly calculate various lengths in geometric problems without resorting to more advanced methods.