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Perimeter of Complex Shapes
5 min readGrade 6 · Measurement
An L-shaped garden isn't a rectangle, but you can still find its perimeter by adding up all the outer edges—or by decomposing it into two rectangles.
What is a complex shape?
A complex shape is made by combining two or more simpler shapes (usually rectangles). It has no holes and no overlapping parts.
Finding perimeter by adding all sides
Count every outer edge. For an L-shape, you might count 6 sides instead of 4. Some side lengths are given; others you figure out using the fact that opposite sides of a rectangle are equal.
Decompose and add
Another strategy: Break the complex shape into two rectangles. Find the perimeter of each (or just the outer edges), then add them together. Both methods give the same answer.
KEY VOCABULARY
Complex shape — A shape made of two or more simpler shapes (usually rectangles) joined together.
Perimeter — The distance around the outside of a shape; the sum of all side lengths.
Decompose — To break a shape into simpler, non-overlapping shapes.