Geometry

Vertical Angles

Proof by a half-turn

  • Primary school
  • about 3 min
  • 2 of 9 in the family
Not started
Vαβγδcommon vertex, arms are opposite rays
Rotate the second lineα = 50°

Rotate α a half turn about the vertex and watch where it lands.

α = γ50°
β = δ130°

Vertical angles share a vertex and their arms are opposite rays. They are always congruent.