Ruler and Compass Construction 8
Parallel Line Through Given Point

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1. Transversal line AC
2. Circle centered at A, through C
3. Circle centered at at C, same radius
4. Circle centered at F, radius CD
5. Parallel line CE

Why it works:
The construction copies the angle CAD to angle ACE, so AC is a transversal of
lines AB and EC with equal alternate interior angles, so line EC is parallel to line AB.