Geometry & measures · Perimeter, area & volume
Chapter 1 · 4
The idea
Area of triangles, parallelograms & trapezia
Why every straight-sided area formula is a rectangle in disguise — base times PERPENDICULAR height, the trapezium average, compound shapes by splitting or subtracting, and why 1 m² is 10 000 cm².
A full journey — read it, play with it, work it, then earn real exam marks. Everything stays on the timeline below.
In this lesson — start anywhere
Geometry & measures · Perimeter, area & volume
Area of triangles, parallelograms & trapezia
Why every straight-sided area formula is a rectangle in disguise — base times PERPENDICULAR height, the trapezium average, compound shapes by splitting or subtracting, and why 1 m² is 10 000 cm².
Why it works
Everything becomes a rectangle
Area counts unit squares, and a rectangle counts them instantly: rows of squares. Every other straight-sided formula comes from turning the shape into a rectangle — shear a parallelogram, double a triangle, double a trapezium. Hold that picture and the formulas stop being separate facts to memorise.Parallelogram: shear it square
Slice the right-angled triangle off one end of a parallelogram and slide it round to the other end — you get a rectangle with the same base and the same vertical height. SoKeep reading — free
The rest of the explanation, plus 2 worked examples you step through move by move.
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