📏 Geometry

Geometry formulas describe the size and shape of things — how much surface a flat shape covers, how far around its edge, how much space a solid takes up — and they come up constantly outside the classroom too, in construction, design, and any field that works with physical dimensions. This section covers area and perimeter for triangles, rectangles, squares, and circles, plus volume and surface area for spheres, cylinders, and cones.

The biggest source of errors here isn't the formulas themselves but mixing up which one applies to which shape, or forgetting whether a given measurement is a radius or a diameter. Each page works through a real numeric example so you can see the formula applied to actual dimensions, not just stated abstractly, and several include the rearranged version of the formula (solving for radius instead of area, for instance) since that's often what a real problem actually asks for.