__Perpendicular bisector__
- a bisector of the segment that is perpendicular to the segment

__Median__ - In a
triangle, a segment that joins a vertex of the triangle and the
midpoint of the opposite side

__Altitude__ - a
segment from the vertex of the triangle to the line containing
the opposite side and perpendicular to the line containing that
side

__Angle bisector__
- In the figure below, the ray QS is the bisector of angle PQR
if S is in the interior of the angle, and angle PQS is congruent
to angle RQS

__Theorem__ - any
point on the perpendicular bisector of a segment is equidistant
from the endpoints of the segment

__Theorem__ - any
point equidistant from the endpoints of a segment lies on the
perpemdicular bisector of the segment

__Theorem__ - any
point on the bisector of an angle is equidistant from he sides
of the angle

__Theorem__ - any
point on or in the interior of an angle and equidistant from the
sides of an angle lies on the bisector of the angle

*Explorations with GSP

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