Geometry
Every lesson explains the concept, works through examples, and gives you practice problems with full solutions. Work through them in order, or jump to the topic you need.
8 lessons
- Perimeter: The Distance Around a ShapeWhat perimeter means, how to find it for any shape by adding the sides, the rectangle shortcut, and how to work backwards from a known perimeter.
- Area of a Rectangle: Length Times WidthWhy the area of a rectangle is length times width, how to find a missing side, why area uses square units, and how to handle L-shaped figures.
- Volume of a Rectangular Prism: Length × Width × HeightWhy the volume of a box is length times width times height, why the units are cubed, and how the base-times-height form works for any prism.
- Area of a Triangle: Half the Base Times the HeightWhy the area of a triangle is half base times height, what counts as the height, and how to handle triangles where the height falls outside the shape.
- Circumference of a Circle: C = πdHow to find the circumference of a circle from its diameter or radius, what pi actually is, and how to work backwards from a known circumference.
- Area of a Circle: A = πr²How to find the area of a circle from its radius or diameter, why the formula squares the radius, and the mistake of using the diameter instead.
- The Pythagorean Theorem: a² + b² = c²How to use a² + b² = c² to find a missing side of a right triangle, why c must be the hypotenuse, and how to find a leg rather than the hypotenuse.
- Parallel and Perpendicular Lines: The Slope RulesParallel lines have equal slopes and perpendicular lines have negative reciprocal slopes — why both rules are true, and how to write equations using them.