Angle Relationships Explorer

Pick a mode and drag the slider to explore how angles relate to each other. See complementary pairs, supplementary pairs, vertical angles, and all eight angles formed by parallel lines with a transversal. All computation runs in your browser.

Angle Relationship

Angle35°

1°89°

Try an example

Angle Relationships

Two angles are complementary when they add up to 90 degrees.

Angle A

35°

Angle B

55°

\angle A + \angle B = 90°

35° + \angle B = 90°

\angle B = 90° - 35°

\angle B = 55°

Reference Guide

Complementary Angles

Two angles are complementary when their measures add up to 90 degrees. They form a right angle together.

\angle A + \angle B = 90°

If one angle is 35 degrees, its complement is $90° - 35° = 55°$ . Complementary angles do not need to be adjacent.

Supplementary Angles

Two angles are supplementary when their measures add up to 180 degrees. They form a straight line together.

\angle A + \angle B = 180°

If one angle is 120 degrees, its supplement is $180° - 120° = 60°$ . Adjacent angles on a straight line are always supplementary.

Vertical Angles

When two straight lines cross, they form two pairs of vertical (opposite) angles. Vertical angles are always equal.

\angle 1 = \angle 3, \quad \angle 2 = \angle 4

Each pair of adjacent angles around the intersection is supplementary (adds to 180 degrees).

Parallel Lines and Transversals

A transversal crossing two parallel lines creates eight angles with these relationships.

Corresponding angles are equal
Alternate interior angles are equal
Alternate exterior angles are equal
Co-interior (same-side) angles sum to 180 degrees

Knowing just one angle lets you find all eight.

TopicsShapes Measurement Trigonometry Geometry Labeled Diagram

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