Cards | 10 |

Topics | Angles Around Lines & Points, Calculations, Coordinate Grid, Dimensions, Quadrilateral, Right Angle, Triangle Classification |

Angles around a line add up to 180°. Angles around a point add up to 360°. When two lines intersect, adjacent angles are **supplementary** (they add up to 180°) and angles across from either other are **vertical** (they're equal).

The **circumference** of a circle is the distance around its perimeter and equals π (approx. 3.14159) x diameter: c = π d. The **area** of a circle is π x (radius)^{2} : a = π r^{2}.

The coordinate grid is composed of a horizontal **x-axis** and a vertical **y-axis**. The center of the grid, where the x-axis and y-axis meet, is called the **origin**.

A circle is a figure in which each point around its perimeter is an equal distance from the center. The **radius** of a circle is the distance between the center and any point along its perimeter (AC, CB, CD). A **chord** is a line segment that connects any two points along its perimeter (AB, AD, BD). The **diameter** of a circle is the length of a chord that passes through the center of the circle (AB) and equals twice the circle's radius (2r).

A quadrilateral is a shape with four sides. The **perimeter** of a quadrilateral is the sum of the lengths of its four sides (a + b + c + d).

A right angle measures 90 degrees and is the intersection of two **perpendicular** lines. In diagrams, a right angle is indicated by a small box completing a square with the perpendicular lines.

An **isosceles** triangle has two sides of equal length. An **equilateral** triangle has three sides of equal length. In a **right** triangle, two sides meet at a right angle.