Geometry
Shape and Angle
Proof-based plane geometry: angles, parallel lines, congruent and similar triangles, right-triangle trigonometry, polygons, circles, area, volume and transformations.
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Where Geometry Begins
Unit 1 · Points, Lines & Planes
0 of 10 units complete
- 1Unit 1Points, Lines & Planes5 parts · about 11 min
Where Geometry Begins
Points, lines and planes are the three words geometry never defines. Measure segments, find midpoints and distances on a grid, and count how many lines a handful of points can make.
- 2Unit 2Angles5 parts · about 10 min
Angle Detective
Name and classify angles, add them up, bisect them, and use linear pairs and vertical angles to find any unknown angle with algebra.
- 3Unit 3Parallel & Perpendicular Lines5 parts · about 11 min
Parallel Lines and a Transversal
A line crossing two parallel lines makes eight angles but only two sizes. Tilt it and watch, learn the angle-pair names, prove lines parallel, and meet the 2,000-year argument over the parallel postulate.
- 4Unit 4Triangles & Congruence5 parts · about 11 min
Triangles You Can Trust
Angles that always add to 180°, the exterior angle shortcut, which sides can make a triangle, and the five shortcuts that prove two triangles are identical — plus why SSA is missing.
- 5Unit 5Transformations5 parts · about 12 min
Slide, Flip, Turn, Stretch
Move a triangle onto a ghost target with translations, reflections, rotations and dilations, discover the coordinate rule for each, and learn which moves keep a shape the same size.
- 6Unit 6Similarity5 parts · about 10 min
Same Shape, Different Size
Similar figures are scaled copies. Find scale factors, prove triangles similar with only two angles, measure a pyramid with a shadow, and discover why giant ants could never exist.
- 7Unit 7Right Triangles & Trig5 parts · about 12 min
The Right-Angle Toolkit
The Pythagorean theorem and its converse, triples that come out whole, the two special right triangles, and SOH-CAH-TOA for everything else — measuring ramps, ladders and lighthouses.
- 8Unit 8Quadrilaterals & Polygons5 parts · about 11 min
Polygons and Their Angles
Why a hexagon's angles add up to 720°, why bees build hexagons, the family tree of quadrilaterals, and the surprising fact that every polygon's exterior angles add to exactly one full turn.
- 9Unit 9Circles5 parts · about 10 min
Circles and Their Secrets
Arcs, sectors, the inscribed angle theorem you can drag into existence, why every angle in a semicircle is right, and the equation that draws a circle on a grid.
- 10Unit 10Area & Volume5 parts · about 10 min
Measuring Space
Areas of any polygon on a grid, composite shapes, surface area and volume of prisms, cylinders, cones and spheres — and Archimedes' favourite discovery, which he asked to have on his tomb.