Alternate Angles Definition

noun
A pair of nonadjacent angles, one on each side of a transversal, that are both interior or both exterior: these paired angles are equal if the lines cut by the transversal are parallel.
Webster's New World

(geometry) The internal angles made by two (parallel) lines with a third, on opposite sides of it.If the parallels AB, CD, are cut by the line EF, intersecting at points G and H, then the angles AGH, GHD, are called alternate angles (as also are the angles BGH and GHC).

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