In any parallelogram ABCD, it is always true that the measures of ∠ABC and ∠BCD…….?
Add up to 180°
Those are same-side interior angles. Opposite sides of a parallelogram are parallel and equal. So, what
you have are two angles that are next to each other in the parallelogram, but are on the interior
of the parallel lines, and on the same side of the transversal (one of the sides of the parallelogram).
Same-side interior angles always add up to 180°.
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