The perpendicular bisector of a side of a triangle is a line perpendicular to the side and passing through its midpoint.
Angle Bisector -- from Wolfram MathWorld
Bisectors of Triangles Assignment - Keller ISD Schools
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Incenter - Point of Concurrency of Angle Bisectors of a Triangle (with proof)
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Incircle and Angle Bisectors of a Triangle
triangle angle bisector theorem – GeoGebra
Angle bisector theorem - Wikipedia
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The Perpendicular Bisectors of a Triangle - Wolfram Demonstrations Project