Angles and their sums
Classify angles by size, read an angle from a protractor, work out a missing angle in a triangle or quadrilateral, and identify vertical and supplementary angles.
Available exercises
Classify an angle by its measure
Given the measure of an angle, name it: acute, right, obtuse or straight.
Measure an angle with a protractor
Read the measure of the angle shown on the protractor. Values are in steps of 10° (from 20° to 160°).
Angle sum in a quadrilateral
You know three angles of a quadrilateral. Work out the fourth — the sum is always 360°.
Angle sum in a triangle
You know two angles of a triangle. Work out the third — the sum is always 180°.
Vertical and supplementary angles
Two crossing lines form pairs of angles. Vertical (opposite) angles are equal; supplementary (adjacent on the same line) angles add to 180°.
Alternate angles on parallel lines
A transversal cuts two parallel lines. Alternate interior angles (on opposite sides of the transversal, between the parallels) are equal.
Corresponding angles on parallel lines
A transversal cuts two parallel lines. Corresponding angles (in the same position at each intersection) are equal.
Interior angle sum of a polygon
Work out the sum of interior angles of an n-gon using the formula (n − 2) · 180°.