Question

1. what must be true about lines n and m in order for angles 1 and 2 to be supplementary?

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Explanation:

Supplementary angles sum to $180^\circ$. When two lines are parallel, same-side interior angles formed by a transversal are supplementary. If lines $n$ and $m$ are parallel, angles 1 and 2 (same-side interior angles) will add up to $180^\circ$.

Answer:

Lines $n$ and $m$ must be parallel.