MA25-08 Maths Coming soon
Writing formal geometric proofs using angle facts (Higher)
MA25-08
This lesson is coming soon.
In this lesson
Structure a chain of angle-fact statements into a formal, logically ordered geometric proof, with a clear reason at every step and no gaps between the given information and the stated conclusion.
What it covers
- What turns a set of true statements about a diagram into a formal PROOF: a logical order building step by step toward the thing being proved, not just a list of facts
- Writing each line as a clear statement-plus-reason pair, using correct angle notation from G-ANGLE-1
- A full model answer to a 'prove that...' angle question, annotated to show why each line earns its mark
- Recognising when a proof is incomplete (true facts stated but no logical chain to the conclusion) versus complete
Key words
For: OCR GCSE J560
On the specification
| Board | Spec | Statement |
|---|---|---|
| OCR GCSE J560 | 8.03a | Know and use the sum of the angles at a point is 360°. |
| OCR GCSE J560 | 8.03b | Know that the sum of the angles at a point on a line is 180°. |
| OCR GCSE J560 | 8.03c | Know and use: vertically opposite angles are equal; alternate angles on parallel lines are equal; corresponding angles on parallel lines are equal. |
| OCR GCSE J560 | 8.03d | Derive and use the sum of the interior angles of a triangle is 180°. Derive and use the sum of the exterior angles of a polygon is 360°. Find the sum of the interior angles of a polygon. Find the interior angle of a regular polygon. |
For teachers
This GCSE Maths lesson teaches writing formal geometric proofs using angle facts (Higher). By the end, students should be able to structure a chain of angle-fact statements into a formal, logically ordered geometric proof, with a clear reason at every step and no gaps between the given information and the stated conclusion. It works through two worked examples and the mistakes examiners report.