Geometry & measures · Constructions & loci
Chapter 1 · 4
The idea
Ruler-and-compass constructions
The four standard constructions — perpendicular bisector, angle bisector, perpendicular from/at a point, and 60° — why each one works, and why the construction arcs must be left on the page.
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 · Constructions & loci
Ruler-and-compass constructions
The four standard constructions — perpendicular bisector, angle bisector, perpendicular from/at a point, and 60° — why each one works, and why the construction arcs must be left on the page.
Why it works
What compasses actually draw
A pair of compasses draws "all the points this far from here". Every standard construction is built from that one idea, so each one can be reasoned rather than memorised — which matters, because the mark scheme rewards the reasoning (the arcs) as much as the finished line.The perpendicular bisector
Open the compasses to more than half of . With the point on , draw arcs above and below; keeping the *same radius*, repeat from . Why the crossings are the right points:Keep reading — free
The rest of the explanation, plus 2 worked examples you step through move by move.
Start freeTakes a minute — no card.