top of page
Same-Side Interior Angles Theorem
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
The Same-Side Interior Angles Theorem states:
“If two parallel lines are cut by a transversal, then the same-side interior angles are supplementary.”
In simpler terms:
When a transversal crosses two parallel lines,
The two angles that are on the same side of the transversal and inside the parallel lines
Will always add up to 180°
Also known as:
The Consecutive Angles Theorem
Example:
If line l is parallel to line m, and a transversal t crosses them:
∠3 and ∠4 are on the same side of the transversal and inside the lines → Then: ∠3 + ∠4 = 180°
Video
bottom of page