**Common formulas in the study of geometry include calculating the perimeter and area of shapes.** For example, the perimeter or outside of a rectangle is the length plus the width of the rectangle times two.

The area of the rectangle is calculated by multiplying the length times the width. The area total is expressed in square inches, feet or whatever the length or width measurement is. A rectangle measuring 5 inches by 3 inches has an area of 15 square inches.

The perimeter of a circle is called a circumference, and it is calculated with the following formula: 2 times the radius times pi. A radius is half the circle's diameter, or half the distance across the middle of a circle. A circle's area is calculated with a similar formula: pi times the radius squared. Thus, a circle with a radius of 10 inches has a circumference of 62.8 inches and an area of 314 square inches.

Geometry is the study of points, lines, angles, surfaces and shapes. Every student of geography learns an important formula or theory called the Pythagorean theorem, which is named after the Greek mathematician Pythogras. He determined that in every triangle with a right angle, a person can calculate the length of the hypotenuse as long as she knows the length of the other two sides. The Pythagorean theorem states that the length of the hypotenuse is calculated by adding side A squared to side B squared, and then dividing that number in half.