The perimeter of a closed plane figure is the length of its boundary. Area of a closed plane figure is the measure of the region (surface) enclosed by its boundary. In a right-angled triangle, the square of the hypotenuse is equal to the sum of the squares of the other two sides. The Area (A) of a closed plane figure is the region of the plane enclosed by the figure's boundary. The Area is measured in square units of length, such as square centimetre (cm2) and square metre (m2). With the usual lettering, the perimeter of a rectangle is 2(L + B), a square is 4L, a circle is 2pir or pid. The perimeter of a circle is called the circumference. The Area of a shape is a measure of its surface.