Math CentralQuandaries & Queries


Question from olivia, a student:


I've forgotten how to work out the perimeter of a shape. can you help me out????

Hi Olivia,

The perimeter of a shape is the distance around the outside of the shape. For example to find the perimeter of the building you live in you could get a tape measure, go outside, start at one place on the building and measure all the way around until you get back to where you started.

Some shapes are easy. If you have a rectangle that is L feet long and W feet wide then measuring all the way around would give you L + W + L + W = 2(L + W) feet. If you have a circle of radius r inches then its perimeter is 2 π r inches where π is approximately 3.1426. If you have half a 12 inch pizza then the perimeter is the length of the curved side plus the length of the straight side so it would be

(2 π r)/2 + 2r = 6 π + 12 inches.

If the outline shape is not composed of straight line segments and pieces of circles then finding the perimeter can be much more difficult.


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