Solid Geometry

Geometry, off the page: how lines and planes behave in space, then the five solid families — prisms, pyramids, cylinders, cones, spheres — their surfaces and volumes, the cuts that reveal them, and the scaling law (k, k², k³) that runs them all. Every 3D problem hides a flat right triangle; this course teaches you to find it, with a diagram at nearly every step.

1. 01Lines & Planes in SpaceThe rules of 3D: what determines a plane, skew lines, perpendicularity, and the two angles every exam measures.Start
2. Premium02Prisms & the CubeThe box family: prism anatomy, the cube's √2 and √3 diagonals, and surface & volume you can see face by face.Start
3. Premium03PyramidsHeight, apothem, slant, edge — the two Pythagorean triangles inside every pyramid, the ⅓ in the volume, and the frustum.Start
4. Premium04Cylinders & ConesThe round solids you can unroll: the cylinder's rectangle label, the cone's pie-slice development, and both volumes.Start
5. Premium05SpheresEvery slice a circle (r² = R² − d²), the surface of exactly four great circles, and Archimedes' tombstone 2:3.Start
6. Premium06Cross-Sections & Similar SolidsPredict any cut, scale with k / k² / k³, glue and drill combined solids — and the five-triangle exam strategy.Start