Standard area formulae
Memorise these. PERPENDICULAR height matters.
Standard formulae:
| Shape | Area |
|---|---|
| Square | |
| Rectangle | |
| Triangle | |
| Parallelogram | |
| Trapezium | |
| Rhombus | (diagonals) |
= PERPENDICULAR HEIGHT (90° to base). Not slant.
If diagram shows slant length, may need Pythagoras to find perpendicular height first.
Worked example. Triangle, base 10, slant side 13, perpendicular height to that base is unknown.
- If you know base 10 and slant side 13 (and these don't form a right angle directly): use Pythagoras with half-base if isosceles, or use other methods.
Edexcel tip. Diagrams sometimes have marked clearly. If not, identify the perpendicular drop from the apex to the base.
- Triangle: .
- Trapezium: .
- All use PERPENDICULAR height.
- Compound: split into rectangles + triangles.