Geometric terms and notation

WJEC awards independent B1 marks for correct labelling — even on Higher reasoning questions, a B-mark is often available simply for naming an angle correctly with three letters.

Core vocabulary

• Point — a location, no size. Single capital letter, e.g. A.
• Line — extends infinitely both ways. Notation: line AB, or lower-case ℓ.
• Line segment — finite part between endpoints. Notation: AB.
• Ray — starts at a point, extends infinitely in one direction.
• Vertex (vertices) — corner where edges meet. A pentagon has 5 vertices.
• Edge — line segment between two vertices.
• Face — flat surface of a 3D solid.
• Plane — flat 2D surface extending infinitely.
• Parallel — never meet. Notation: AB ∥ CD or matching arrowheads on diagrams.
• Perpendicular — meet at 90°. Notation: AB ⊥ CD or right-angle square.

Naming angles — three-letter notation

The middle letter is always the vertex. ∠ABC is the angle at vertex B, between rays BA and BC. ∠CBA is the same angle.

WJEC frequently writes single-letter angles as a^, x or labels them with arc marks. When asked to "name" an angle, always supply three letters unless the question gives a single-letter symbol.

Polygon and triangle naming

Triangle ABC has vertices listed in order — clockwise or anticlockwise around the perimeter. For congruence △ABC ≡ △PQR, A↔P, B↔Q, C↔R, so AB = PQ, BC = QR, AC = PR.

WJEC diagram conventions

• Right-angle: small square in the corner.
• Equal lengths: matching tick marks.
• Equal angles: matching arc marks.
• Parallel: matching arrowheads.
• "Diagram not drawn to scale" — never measure with ruler/protractor; use given values.

Exam tip

When asked "give a reason", quote the exact rule in standard wording — "alternate angles are equal", "angles on a straight line sum to 180°". A correct number with no quoted reason loses the SC1/B1 communication mark on Higher reasoning items.