Perimeter can be calculated by breaking up a composite shape into simple shapes and adding up their lengths. Watch the video to see calculating the perimeter of an ice rink.
Parallelograms, Trapezoids, Hexagons, Octagons and other geometric shapes can be broken up into triangles and rectangles. Their perimeters can also be calculated by adding up the appropriate side lengths of those triangles and rectangles.
Perimeter calculations involve using the Pythagorean formula. The length of the hypotenuse side (c) must be calculated and added to sides (a) and (b). Labels on the legs or sides (a) and (b) are interchangeable, but side (c) must be the one opposite the right (90°) angle. See more about angles in episode 30.
Perimeter = a + b + c
Length of side (c) calculation uses the Pythagorean formula a2 + b2 = c2, so
What is the perimeter of a triangle with legs a = 7 in, b = 4 in?
Perimeter = a + b + c = 7 + 5 + 8.062 = 20.062 in