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Illustration of angles with parallel sides. "GH is parallel to and lies in the same direction as DE, and HI is parallel to but lies in the opposite direction to EF; hence, angle GHI is the supplement of DEF."

Angles With Parallel Sides

Illustration of angles with parallel sides. "GH is parallel to and lies in the same direction as DE,…

Illustration used to prove the theorem, "Two angles whose sides are parallel, each to each, are either equal or supplementary."

2 Angles With Parallel Sides Theorem

Illustration used to prove the theorem, "Two angles whose sides are parallel, each to each, are either…