In geometry, in a two-dimensional plane, two lines are said to be parallel if they do not intersect, in spite of how much they are extended. For example, opposite sides of a square are parallel.

Angle Properties

In the image to the right,

• All of the red acute angles are congruent
• All of the blue obtuse angles are congruent
• 3 and 6 are alternate interior angles
• 4 and 5 are alternate exterior angles.
• 3 and 7 are corresponding angles.
• 4 and 8 are corresponding angles
• 1 and 5 are corresponding angles
• 2 and 6 are corresponding angles