Mathematics·Mensuration · NSSCO 4.1
Perimeter & area of plane shapes
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Perimeter is the distance all the way around a shape; area is the flat space inside it. In this lesson we find the perimeter of rectangles, squares, triangles and compound shapes, then build up every area formula you need — rectangle, triangle, parallelogram and trapezium. We split composite shapes into simple pieces, convert between square units, and finish with real Namibian money problems: tiling a floor, painting a wall and fencing a garden.
What you'll learn in this lesson
By the end you should be able to (NSSCO Mathematics 4.1):
- Find the perimeter of rectangles, squares, triangles and compound (composite) shapes by adding all the sides
- Recall and use the area formulae for a rectangle (l × w) and a triangle (½ × b × h)
- Recall and use the area formulae for a parallelogram (b × h) and a trapezium (½(a + b) × h), using the perpendicular height
- Find the area of compound shapes by splitting them into simple shapes and adding, or by subtracting a missing piece
- Convert between units of area by squaring the multiplier (e.g. 1 m² = 10 000 cm²)
- Solve problems in context, including the cost in Namibian dollars of tiling, painting and fencing
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