Chapter 13: Geometrical Constructions

Geometrical Constructions applies the circle and triangle theorems from earlier in Class 9 to physical construction — specific angles like 60°, 30° and 45° built from combinations of each other, and triangles built from given sides, angles, and the sum or difference of two sides — using nothing but a compass and straightedge.

Not keeping the compass width fixed between steps that need the same radius is what usually throws off an entire construction. Every method here also needs a justification for why it produces the correct result, not just the steps themselves — that justification is often exactly what separates a full-marks answer from a partial one.