-a presentaion used in one of my local demonstrations as a student-teacher.

4. Altitude
An altitude of a triangle is a
perpendicular segment from a vertex of
the triangle to the opposite side or to
the line containing the opposite side.

7. Median
A median is a segment whose
endpoints are a vertex of the triangle
and the midpoint of the opposite side.

10. Angle Bisector
An angle bisector of a triangle is a
segment which bisects an angle and
whose endpoints are a vertex of the
triangle and a point on the opposite
side.

13. Perpendicular Bisector
A perpendicular bisector of a side of a
triangle is a line perpendicular to the
sides at its midpoint and it is
equidistant to the endpoints of the
given segment.

15. A triangle has 3
altitudes, 3 medians, 3
angle bisectors and 3
perpendicular bisectors.