Parallel Lines, and Pairs of Angles

Testing on Pair of Angles

If Any Pair Of ... Example: Corresponding Angles are equal, or a = e Alternate Interior Angles are equal, or c = f Alternate Exterior Angles are equal, or b = g Consecutive Interior Angles add up to 180° d + f = 180° ... then the lines are Parallel

Transveral

is a line that crosses at least two other lines.

Parallel Lines

Lines are parallel if they are always the same distance apart (called "equidistant"), and will never meet. Parallel lines also point in the same direction.

Example 2

These lines are not parallel, because a pair of Consecutive Interior Angles do not add up to 180° (81° + 101° =182°)

Example 3

These lines are parallel, because a pair of Alternate Interior Angles are equal

Example 1

These lines are parallel, because a pair of Corresponding Angles are equal.

Pair of Angles

When parallel lines get crossed by another line (which is called a Transversal), you can see that many angles are the same, as in this example: These angles can be made into pairs of angles which have special names.

Corresponding Angles

When two lines are crossed by another line (called the Transversal)

Alternate Interior Angles

When two lines are crossed by another line (called the Transversal):

Consecutive Interior Angles

When two lines are crossed by another line (called the Transversal):