Each shape has its own area rule. Rectangle: length × width. Parallelogram: base × perpendicular height. Triangle: ½ × base × height. Trapezoid: ½ × (a + b) × height, where a and b are the parallel sides.
Lengths can be decimals: a rectangle 29.5 cm by 17 cm has area 501.5 cm². For a shape made of several parts, split it, find each area and add them, or find a bigger rectangle and subtract the missing piece.
Worked example
A triangle has a base of 23.5 cm and a height of 7 cm. Find its area.
- Area = ½ × base × height.
- ½ × 23.5 × 7 = 82.25.
Answer:82.25 cm²
Key words
- trapezoid
- a quadrilateral with one pair of parallel sides
- perpendicular
- at a right angle
- composite shape
- a shape made of simpler shapes
Practise this
New questions every time.
Common Core-referenced: 7.G.B.6