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Same-Side Interior Angles (Consecutive Angles)
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 interior angles are:
“A pair of angles that are on the same side of the transversal and between the two lines it intersects.”
Key characteristics:
They are inside the two lines
On the same side of the transversal
Also called consecutive interior angles
Important fact:
If the two lines are parallel, then same-side interior angles are supplementary — meaning their measures add up to 180°.
Example:
If line l is parallel to line m and transversal t crosses them, then:
∠3 and ∠4 form a pair of same-side interior angles, and ∠3 + ∠4 = 180°.
Video
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