A geometric figure is closed if the entire boundary of the figure is part of the figure.^{[1]}  

The clearest example of this is a graph of inequalities. Figure 1 is the graph of a system of inequalities. The points on the line y < 3  x is part of the boundary. However, since the inequality y < 3  x does not include the points on the line, the shaded geometric figure is not closed.  

In figure 2, the inequality y <= 3  x does include the points on the line, so the shaded geometric figure is closed. 
#  A  B  C  D 
E  F  G  H  I 
J  K  L  M  N 
O  P  Q  R  S 
T  U  V  W  X 
Y  Z 
All Math Words Encyclopedia is a service of
Life is a Story Problem LLC.
Copyright © 20052011 Life is a Story Problem LLC. All rights reserved.
This work is licensed under a Creative Commons AttributionNoncommercialShare Alike 3.0 License