All Tools

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

35°
1°89°

Try an example

35°55°

Angle Relationships

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

Angle A

35°

Angle B

55°

∠A+∠B=90°\angle A + \angle B = 90°
35°+∠B=90°35° + \angle B = 90°
∠B=90°−35°\angle B = 90° - 35°
∠B=55°\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.

∠A+∠B=90°\angle A + \angle B = 90°

If one angle is 35 degrees, its complement is 90°−35°=55°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.

∠A+∠B=180°\angle A + \angle B = 180°

If one angle is 120 degrees, its supplement is 180°−120°=60°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.

∠1=∠3,∠2=∠4\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.