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Same-Side Exterior Angles

Same-Side Exterior Angles

One-page printable reference

See It in Action

Two examples of the idea done right—and one common look-alike that is not right.

EXAMPLE

EXAMPLE

NON-EXAMPLE

Definition

In Geometry, same-side exterior angles are:


“A pair of angles that are on the same side of the transversal and outside the two lines it intersects.”

Key characteristics:

  • They are outside the two lines

  • On the same side of the transversal

  • Also called consecutive exterior angles

Important note:

If the two lines are parallel, then same-side exterior angles are supplementary (their measures add up to 180°).

Example:

If line l is parallel to line m, and transversal t crosses them, then:

  • ∠1 and ∠2 form a pair of same-side exterior angles, and ∠1 + ∠2 = 180°.


Two parallel lines labeled l and m cut by transversal t. Two angles are marked and labeled 1 and 2. Angle 1 is in the top right of the upper angle section, and angle 2 is in the bottom right of the bottom angle section.

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