Area · Grade 8

In Grade 8 you learn: units of area.

Area is the amount of flat space a shape covers, measured in square units such as cm² and m². Count the squares, or use the formula for the shape; a compound shape splits into simpler shapes.

Key facts

Triangle: area = ½ × base × perpendicular height.
Parallelogram: area = base × perpendicular height.
Trapezoid: area = ½ × (a + b) × h, where a and b are the parallel sides.

Worked examples

Example 1

A triangle has a base of 10 cm and a perpendicular height of 7 cm. Find its area.

Answer: 35 cm²

Example 2

A trapezoid has parallel sides of 6 cm and 10 cm and a height of 5 cm. Find its area.

Answer: 40 cm²

Example 3

A trapezoid has an area of 36 cm² and parallel sides of 5 cm and 7 cm. Find its height.

Answer: 6 cm

Example 4

A circle has a radius of 5 cm. Find its area to 1 decimal place.

Answer: 78.5 cm²

Example 5

Find the area of a parallelogram with a base of 8 cm and a perpendicular height of 5 cm.