Angle facts, parallel lines, triangles, quadrilaterals and polygons, symmetry, congruent and similar figures, ruler-and-compass constructions and solids.
6 narrated scenes. Press play, listen and read along — the points appear as they are explained. Use ‹ Prev / Next › or the scene bar to jump to any scene.
“Give a reason for each statement.” Geometry in CSEC is half calculation, half argument — and every argument uses the same short list of facts.
Narration uses your device’s built-in voice. No sound? Switch to “Captions only” — the captions advance on their own.
Parallel lines and angle pairs; angle sums in polygons.
Copy these into your notebook in your own words — that is how they stick.
Straight line 180°; point 360°; vertically opposite equal; complementary 90°; supplementary 180°.
Corresponding and alternate angles equal; co-interior add to 180°. Always give the reason.
Angles add to 180°; exterior angle = sum of interior opposite; isosceles base angles equal.
Angles add to 360°; know the properties of square, rectangle, rhombus, kite, parallelogram, trapezium.
Interior sum (n − 2) × 180°; exterior sum 360°; regular: exterior 360/n.
Lines of symmetry; rotational order. Regular n-gon: n lines and order n.
Congruent: SSS, SAS, ASA/AAS, RHS. Similar: equal angles, ratio of sides k; area ratio k²; volume ratio k³.
Perpendicular bisector, angle bisector, 60° and 90° angles; keep arcs; V − E + F = 2 for solids.
3 quick games on this lesson. Earn XP and badges as you play — your best score for each game is saved. Games are for practice and do not change your exam readiness. More games in the Mathematics Arcade.
8 items modelled on real CSEC Paper 1 questions. Choose one answer for each, then check. Aim for 80% or better. Work each item on paper first.
Write full answers, then reveal the mark scheme and tick the points you earned (18 marks in total). Show all your working — method marks count. Your answers are saved on this device.
Question 1 [9 marks]
ABCDEFGH is a regular octagon.
(a) State the number of lines of symmetry and the order of rotational symmetry of the octagon. [2]
(b) Calculate the size of one exterior angle and show that one interior angle is 135°. [3]
(c) Two parallel lines are cut by a transversal. One of the angles formed is 112°. Write down the size of (i) the vertically opposite angle, (ii) a corresponding angle, (iii) a co-interior angle to it, with a reason for each. [4]
Question 2 [9 marks]
Triangles ABC and PQR are similar. AB = 6 cm, PQ = 9 cm and BC = 8 cm. The area of triangle ABC is 20 cm².
(a) Find the length of QR. [2]
(b) Find the area of triangle PQR. [3]
(c) Using ruler and compasses only, construct triangle XYZ with XY = 7 cm, YZ = 6 cm, XZ = 5 cm, then construct the perpendicular bisector of XY. (Check your drawing: sides accurate to 1 mm, construction arcs shown, bisector passes through the midpoint at right angles.) [4]
Find these in your own past-paper booklets for extra timed practice. Items above are written in the style of these papers; any adapted from a specific question say so.