Area of Polygons
Calculating areas of complex polygons builds on basic shapes. Year 8 students find areas of composite shapes, trapezoids, and irregular polygons by combining and subtracting familiar shapes.
What You Need to Know
Key Concept Diagram
Area of a trapezoid: A = 1/2 x (a + b) x h, where a and b are parallel sides
Composite shapes can be split into rectangles, triangles, and other known shapes
Subtract the area of a cutout from the total to find composite areas
Always check units: area is measured in square units (cm2, m2, km2)
Key Vocabulary
Trapezoid
A quadrilateral with exactly one pair of parallel sides
Composite shape
A shape made by combining two or more simple shapes
Perpendicular height
The height measured at a right angle to the base
Perimeter
The total distance around the outside of a shape
Knowledge Check
Select the correct answer for each question. Click "Check Answer" to see if you are right.
Question 1
A trapezoid has parallel sides of 8 cm and 12 cm, and a perpendicular height of 5 cm. What is its area?
Question 2
A composite shape is an 8x6 rectangle with a 2x3 rectangle removed from one corner. What is its area?
Question 3
Which formula gives the area of a triangle?
Key Concepts Summary
- ●Area of a trapezoid: A = 1/2 x (a + b) x h, where a and b are parallel sides
- ●Composite shapes can be split into rectangles, triangles, and other known shapes
- ●Subtract the area of a cutout from the total to find composite areas
- ●Always check units: area is measured in square units (cm2, m2, km2)