| − | In plane geometry, the '''perimeter''' of a 2-dimensional object is equal to the length of the object's boundary. For example, the perimeter of a [[polygon]] is the sum of the lengths of its sides. The perimeter of a circle is its [[diameter]] multiplied by [[pi]]. | + | In plane geometry, the '''perimeter''' of a 2-dimensional object is equal to the length of the object's boundary. For example, the perimeter of a [[polygon]] is the sum of the lengths of its sides. The perimeter of a circle is called a [[circumference]], and is the circle's [[diameter]] multiplied by [[pi]]. |