Module 10 of 30Lesson 1 of 6 · G-F1 The Vocabulary of Shapes
Geometry strand · Unit G-F1 · Builds towards C4.1

The Vocabulary of Shapes

🟢 Foundation levelLearn the names, earn the marks

1 Learn it

Geometry pays marks for KNOWING NAMES. The exam-required vocabulary:

Triangles: equilateral (3 equal sides) · isosceles (2 equal) · scalene (none equal) · right-angled.

Quadrilaterals: square · rectangle · parallelogram (opposite sides parallel & equal) · rhombus (a pushed-over square: 4 equal sides) · kite (2 pairs of adjacent equal sides) · trapezium (ONE pair of parallel sides).

Polygons: pentagon 5 · hexagon 6 · octagon 8 · decagon 10 — regular means all sides AND angles equal.

Solids: cube, cuboid, prism, cylinder, pyramid, cone, sphere — with faces, edges and vertices.

🔑 Circle vocabulary (a favourite label-the-diagram question): radius centre-to-edge · diameter edge-to-edge through the centre · circumference the perimeter · chord edge-to-edge NOT through the centre · tangent touches at exactly one point · arc part of the circumference · sector a pizza slice (two radii) · segment chord-cut piece.
radius chord tangent The tangent touches at ONE point only
Radius (teal), a chord (terracotta) and a tangent (green) touching the circle once.

2 Watch it work
EXAMPLE 1

A triangle has sides 5 cm, 5 cm and 8 cm. Name its type.

Two equal sides → isosceles.

EXAMPLE 2

Which quadrilateral has 4 equal sides but no right angles?

Rhombus — the pushed-over square.

EXAMPLE 3

How many faces, edges and vertices has a cuboid?

6 faces, 12 edges, 8 vertices — count them on any box of matches.

EXAMPLE 4

A line joins two points on a circle without passing through the centre. Name it — and what would it be called if it DID pass through the centre?

A chord; through the centre it becomes the diameter (the longest possible chord).

3 Your turn — try first, then reveal
🚫 No calculator[1 mark]

Q1. Name the triangle with all three sides equal.

👀 Show answer
✍️ How your working should look in the exam
equilateral   ✓ B1
Why this works
Equal-lateral = equal sides — and its three angles are all 60°.

🚫 No calculator[1 mark]

Q2. Which quadrilateral has exactly ONE pair of parallel sides?

👀 Show answer
✍️ How your working should look in the exam
trapezium   ✓ B1
Why this works
Parallelograms have two pairs; the trapezium keeps just one.

🚫 No calculator[1 mark]

Q3. How many sides has a decagon?

👀 Show answer
✍️ How your working should look in the exam
10   ✓ B1
Why this works
Deca = ten (like a decade).

🚫 No calculator[1 mark]

Q4. Name the straight line that touches a circle at exactly one point.

👀 Show answer
✍️ How your working should look in the exam
tangent   ✓ B1
Why this works
One touch, never crossing — see the green line in the diagram.

🚫 No calculator[2 marks]

Q5. What is the difference between a sector and a segment of a circle?

👀 Show answer
✍️ How your working should look in the exam
sector = region between two radii (pizza slice)   ✓ B1
segment = region cut off by a chord   ✓ B1
Why this works
SeCtor from the Centre; seGment cut by a chord. The wordplay sticks.

🚫 No calculator[1 mark]

Q6. An angle of 245° is called…

👀 Show answer
✍️ How your working should look in the exam
reflex   ✓ B1
Why this works
Acute < 90° · right = 90° · obtuse 90–180° · REFLEX beyond 180°.

4 Common mistakes — don’t lose easy marks
  • Rhombus vs parallelogram: the rhombus needs all FOUR sides equal.
  • Chord vs diameter: the diameter is the special chord through the centre.
  • Sector/segment swapped: seCtor–Centre, seGment–chord.
  • Vertex/edge/face confused on solids: corners are vertices, lines are edges, flats are faces.
5 Where this leads

Every geometry answer that gives a REASON needs this vocabulary spelled correctly. Circle words return with force in the circle theorems (G-C7, G-E2, G-E3). Next: using your hands — measuring and drawing.

✅ Take the Check Yourself quiz below, then continue to G-F2 Measuring and Drawing.

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