Geometry

Basic geometric terms

An overview of the basic geometric terms assumed in other articles: point, line, line segment, ray, plane and angle.

Line

A line and its properties. Describing a line in the plane, graphically and algebraically, converting between the two, and the relative positions of two lines.

Angles

What an angle is and how its size is measured. Special pairs of angles, adding and subtracting angles, copying an angle, and constructing an angle bisector.

Square

The square and its properties: sides, diagonals, perimeter and area. How to draw a square, the circumcircle and incircle, and what a square metre is.

Rectangle

The rectangle and its properties: sides, interior angles and diagonals. Perimeter and area of a rectangle, the circumcircle and incircle, and the link to the square.

Areas and volumes

An overview of formulae for perimeter, area and volume. Square, rectangle, parallelogram, trapezium, triangle, circle, cube, sphere, cylinder and pyramid.

Triangles

How to construct a triangle when you know three sides, two sides and an altitude, or two sides and a median. The construction step by step.

Circles

What a circle is, how it is labelled and what its parts are. Radius, diameter, chord, circumference and area, the positions of two circles relative to each other, and the angle at the centre and at the circumference.

Formulae: perimeter

How to work out the perimeter of a square from the length of its side. The formula for the sum of all four sides and a worked example with a diagram.

Formulae: area

How to find the area of a square from the length of its side. The formula and a worked example with a diagram.

Formulae: volume

How to work out the volume of a sphere from its radius. The formula and a step-by-step worked example.

Conic sections

Conic sections are formed when a plane cuts the curved surface of a right circular cone. The circle, ellipse, parabola and hyperbola: how they are formed and how they differ.