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Mathematics · Glossary

What is Angle pairs?

Also known as: vertically opposite angles · alternate angles

Definition 51.1 Primary & Middle School Mathematics · Chapter 51 — Triangles and Angles
  • Two angles are complementary when their measures add up to 90∘90^\circ, supplementary when they add up to 180∘180^\circ.
  • When two lines cross, the angles facing each other across the crossing point are vertically opposite.
  • When a line crosses two other lines, angles located in the same position at each crossing are corresponding angles; angles between the two lines on opposite sides of the crossing line are alternate angles.
Left: vertically opposite angles 1 = 3 (each is supplementary to 2). Right: parallel lines cut by a third line — the corresponding angles a and b are equal.
Left: vertically opposite angles 1^=3^\widehat 1 = \widehat 3 (each is supplementary to 2^\widehat 2). Right: parallel lines cut by a third line — the corresponding angles a^\widehat a and b^\widehat b are equal.
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