Mathematics Class 8
Quadrilaterals
Name a shape by what it proves, and build one from measurements.
15 lessons · ~104 min total
Track progress — 0 of 15 lessons read 0%
Lessons in this topic
- 0 Start here A roadmap: four sides joined up, a corner total that never moves, diagonals, five names, and building one from measurements. · 4 min You are here
- 1 Four straight sides, joined up A quadrilateral is four straight sides joined into a closed path, with no side cutting through another. · 6 min
- 2 The four angles come to 360° A diagonal inside the shape cuts it into two triangles, so its four angles total exactly 360°, however the shape is pushed about. · 7 min
- 3 A line to the corner across A diagonal joins two corners that are not neighbours, and a quadrilateral has exactly two of them. · 6 min
- 4 Five names and what each one demands Trapezium, parallelogram, rectangle, rhombus and square are five lists of demands, and a shape earns a name by meeting the whole list. · 8 min
- 5 What a parallelogram gives you Once both pairs of sides are parallel, opposite sides match, opposite angles match, and next-door angles total 180°. · 8 min
- 6 Checkpoint: sides, angles and the family A graded check on the first five ideas — what counts as a quadrilateral, the 360° total, diagonals, the five names, and what a parallelogram hands you. · 6 min
- 7 Diagonals that cut each other in half In a parallelogram the two diagonals cross at a point that is halfway along both of them, and that is a separate fact from their lengths. · 7 min
- 8 A rectangle also has matching diagonals A parallelogram whose diagonals are equal is a rectangle, and equal diagonals on their own are not enough to say so. · 7 min
- 9 A rhombus crosses at a right angle A parallelogram with four equal sides has diagonals that cross at exactly 90°, whatever its corners measure. · 7 min
- 10 One shape, several names The names sit inside one another: every square is a rhombus and a rectangle, every rectangle and rhombus is a parallelogram, and every parallelogram is a trapezium. · 8 min
- 11 Building one from measurements Four side lengths do not settle a quadrilateral, so a construction needs a fifth measurement across the middle. · 9 min
- 12 Checkpoint: diagonals, names and building A graded check on the second five ideas — halving, matching lengths, the square crossing, several names at once, and building from measurements. · 6 min
- 13 The big picture Ten ideas, one cheat sheet. · 6 min
- 14 Track quiz Cheat-sheet table plus a reveal quiz — one question per idea. · 9 min
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