• Vertical angles  are formed when 2 lines intersect. They are called vertical angles. Angle 1 and 3 are equal and angle 2 and 4 are equal. See diagram below.

• Transversal  is when 1 line crosses 2 other lines. The example below is a transversal where 2 lines b and a are parallel. Line c crosses b and a. See diagram below.

• Big angles equal Big angles
• Little angles equal little angles
• A big plus a little angle is 180 degrees or supplemental.