Perimeters of Composite Figures
Perimeters of composite figures is a Grade 7 geometry skill in Big Ideas Math Advanced 2, Chapter 13: Circles and Area. To find the perimeter, trace only the outer boundary of the entire composite figure and sum all exterior edge lengths, being careful to exclude any interior edges where component shapes connect. For example, when a triangle sits on top of a square, the shared base of the triangle is an interior edge and not included in the perimeter.
Key Concepts
To find the perimeter of a composite figure, you can decompose it into simpler shapes and carefully identify which sides form the outer boundary. The perimeter is the sum of all the lengths of the sides that make up the exterior edge of the composite figure.
Common Questions
How do you find the perimeter of a composite figure?
Trace around the outer boundary of the entire figure and add up all the edge lengths that form the exterior. Do not include any interior edges where shapes are joined together.
What edges are excluded when finding perimeter of a composite figure?
Interior edges — the sides where two component shapes are connected and become hidden inside the composite figure — are excluded from the perimeter calculation.
How do you find the perimeter of an L-shaped figure?
Identify all outer boundary edges of the L-shape and add their lengths. Interior edges where the two rectangles join are not included.
What textbook covers perimeters of composite figures in Grade 7?
Big Ideas Math Advanced 2, Chapter 13: Circles and Area covers finding perimeters of composite figures by identifying exterior edges.