Lesson 1: Angles & Polygons Vocab & Formulas

08 Mathematics

Acute angle

An angle that measures less than 90 degrees.

Right angle

An angle that measures exactly 90 degrees.

Obtuse angle

An angle that measures greater than 90 degrees but below 180 degrees.

Straight angle

An angle that measures exactly 180 degrees.

Reflex angle

An angle that measures greater than 180 degrees but below 360 degrees.

Complementary angles

Two angles that sum up to 90 degrees.

Supplementary angles

Two angles that sum up to 180 degrees.

Angles on a straight line

Always sum up to 180 degrees.

Angles around a point

Always sum up to 360 degrees.

Vertically Opposite Angles

Angles that are equal when two straight lines cross.

Equilateral triangle

A triangle with 3 equal sides and interior angles of 60 degrees each.

Isosceles triangle

A triangle with 2 equal sides and two equal interior angles.

Scalene triangle

A triangle with no equal sides and no equal interior angles.

Acute triangle

A triangle in which all three interior angles measure less than $90^\circ$.

Right triangle

A triangle that has one interior angle measuring exactly $90^\circ$.

Obtuse triangle

A triangle that has one interior angle measuring greater than $90^\circ$ and less than $180^\circ$.

Missing Angle in Triangles

Calculated as 180 - Sum of the known angles.

Quadrilateral

A four-sided polygon whose interior angles sum up to 360 degrees.

Square

A quadrilateral with 4 equal sides and each angle measures 90 degrees.

Rectangle

A quadrilateral with two pairs of equal opposite sides and 4 interior angles of 90 degrees.

Parallelogram

A quadrilateral with two pairs of parallel and equal sides, and equal opposite angles.

Rhombus

A quadrilateral with four equal sides and equal opposite angles.

Trapezium

A quadrilateral with one pair of parallel sides.

Kite

A quadrilateral with two pairs of adjacent equal-length sides and one pair of equal opposite angles.

Sum of Interior Angles of a Polygon

Calculated as (n - 2) x 180 degrees, where n is the number of sides.

Interior Angle of a Polygon

Calculated by dividing the sum of angles by n.