# Angles with Parallel or Perpendicular Arms are Equal or Supplementary

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## Theorem

Let $A$ and $B$ be angles such that their corresponding arms are either parallel or perpendicular.

Then $A$ and $B$ are either equal or supplementary.

## Proof

## Sources

- 1968: M.N. Aref and William Wernick:
*Problems & Solutions in Euclidean Geometry*... (previous) ... (next): Chapter $1$: Triangles and Polygons: Theorems and Corollaries $1.6$: Corollary