alternate angles

plural noun

, Geometry.

two nonadjacent angles made by the crossing of two lines by a third line, both angles being either interior or exterior, and being on opposite sides of the third line.

alternate angles

two angles at opposite ends and on opposite sides of a transversal cutting two lines

alternate angles

Two angles formed on opposite sides of a line that crosses two other lines. The angles are both exterior or both interior, but not adjacent.

First recorded in 1650–60

Frustules oblong or quadrate, adnate in filaments, attached by alternate angles and finally separating.

We may now state Prop. 16 thus:—If two straight lines which meet are cut by a transversal, their alternate angles are unequal.

And “if the lines are parallel, are alternate angles necessarily equal?”

That is to say, “If alternate angles are unequal, do the lines meet?”

If two straights make with a transversal equal alternate angles they have a common perpendicular.

April 25, 2024firkin

[fur-kin ]

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