5.4

There were 2 theorems in 5.4, triangle inequality thm. and short distance thm. The triangle inequality thm. states that the sum of the lengths of any 2 sides of a triangle is greater that the length of the third side.

The short distance thm. states that the perpendicular segment from a point to a line is the shortest segment from the point to the line.


Also in 5.4 you have the corollary which states that the perpendicular segment from a point to a plane is the shortest segment from the point to the plane.