Illustration showing that the sum of all the angles about a point equals 360°.

Illustration showing that angles 1 and 2 are complementary.

Illustration showing that the sum of angle 1 and angle 2 is angle ABC.

Illustration showing that angles 1 and 2 are supplementary.

Illustration showing that angles 1 and 2 are vertical and angles 3 and 4 are vertical.

Illustration used to prove the theorem, "The sum of the angles of any triangle is two right angles."