Fiducia TogetherGeometric reasoning
Proving an angle or a property using stated rules. The marks are for the reasons, not the number.
Please note: This page explains a word or a process in education. It is general information about the system, the law and the guidance in England — not advice about your child, your school or your exam. If a decision is going against you, get advice from one of the free services we link to before you agree to anything or miss a deadline. If you are revising, check your own exam board's specification: boards word things differently and yours is the one that marks you.
What it is
Reasoning questions ask you to find an angle or show a property and give reasons at each step, using standard facts about angles, parallel lines, triangles and polygons.
Where it applies
Both tiers, increasingly at Higher.
How it works
The building blocks are worth knowing by name: angles on a straight line, angles around a point, vertically opposite angles, alternate and corresponding angles on parallel lines, the angle sum of a triangle and of a polygon, and the properties of isosceles and equilateral triangles.
How to use it in your work
Write a reason for every step, in the standard wording. "Alternate angles are equal" is a mark; "they're the same" is not.
Do not measure the diagram. Diagrams are explicitly not to scale and measuring scores nothing.
Where to get help
Your teacher, your board's specification for what is on your paper, and Bitesize for worked examples. The maths song runs the topics in order.
Revise this with a song
These are ours. We write revision songs because a lot of people remember a tune when they cannot remember a page, and because revising out loud in the kitchen beats staring at a highlighter.
- The Maths Song The GCSE maths topics, in order.
Where to read more
Last reviewed 2026-08-28 by Fiducia Together · Next review due 2027-08-28
Please note: This page explains a word or a process in education. It is general information about the system, the law and the guidance in England — not advice about your child, your school or your exam. If a decision is going against you, get advice from one of the free services we link to before you agree to anything or miss a deadline. If you are revising, check your own exam board's specification: boards word things differently and yours is the one that marks you.