Identifying Outer Perimeter Edges
Identifying outer perimeter edges is a Grade 7 geometry skill in Big Ideas Math Advanced 2, Chapter 13: Circles and Area, focused on composite figures. Only the outer boundary edges count toward the perimeter — interior edges where component shapes connect are not included in the calculation. For example, in an L-shaped figure, the edges where the two rectangles join are interior edges and must be excluded.
Key Concepts
The perimeter of a composite figure includes only the outer edges that form the boundary of the entire shape. Interior edges where component shapes connect are not part of the perimeter calculation.
Common Questions
What edges count toward the perimeter of a composite figure?
Only the outer boundary edges that form the exterior of the entire composite figure count. Any edges shared between component shapes are interior edges and are not included in the perimeter.
How do you identify interior edges in a composite figure?
Interior edges are the sides where two shapes are joined together and become hidden inside the composite figure. These shared boundaries are not part of the perimeter.
Why is identifying outer perimeter edges important?
Failing to exclude interior edges leads to double-counting shared boundaries, which gives an incorrect perimeter. Always trace only the outer boundary of the complete figure.
What textbook covers perimeter of composite figures in Grade 7?
Big Ideas Math Advanced 2, Chapter 13: Circles and Area covers identifying outer perimeter edges and composite figure geometry.