 Manipulative 1: Altitude. Created with GeoGebra. 

An altitude is the shortest distance from a
vertex
of a geometric figure to a line containing the opposite side (2D) or the base (3D).^{[1]} The altitude is always
perpendicular
to the opposite side. The foot of an altitude is
the point where the altitude intersects the line containing the opposite side.
Manipulative 1 shows the altitudes of a triangle. Click on the blue points and
drag them to change the figure. The red lines are the altitudes. The dotted lines
are the lines which contain the opposite side. The feet of the altitude are the
purple dots. Click on the
reset button to return the manipulative to its original configuration.
Discovery
 For what type of triangle is the foot of an altitude not on the leg
of the triangle?
 For what type of triangle does the altitude coincide with a leg of the triangle?
 For what type of triangle does the altitude intersect the opposite side?
