Count filled unit squares for area and exposed edges for perimeter.
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First lesson in this subject: Complete the angle sum
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On a unit grid, each filled square contributes 1 square unit of area. Perimeter is the length around the outside, measured in units. Internal edges do not belong to the perimeter.
A rectangle three squares wide and two high has area 6 and perimeter 3 + 2 + 3 + 2 = 10. Count cells for one measurement and exposed edges for the other.
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First lesson in this subject: Complete the angle sum
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Practice · Build connected shapes with a fixed area. Match a target perimeter, or find the smallest or largest possible perimeter.
Book · Explore measurements, transformations, coordinates and geometric relationships through diagrams and worked examples.
Previous lesson · Measure perpendicular height to compare triangle areas without relying on shape.
Next lesson · Distinguish the scale factor for side lengths from the scale factor for area.
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