



The
next group of definitions, postulates, and theorems



has to do
with our old pal the double cross. 





Let's
review that double cross. 


Draw two
parallel lines and a line that crosses them. 


Label all
the angles with letters. 


Like
this: 











We know
two things about this. 


We know
that: 


A
= C = E = G and B = D = F = H






We also
know that: 





If A = B = C =
D, the crosses are perpendicular. 











Math
types took this one little trick 


and
turned it into a ton of definitions, theorems, and postulates 


(or
axioms). 





DEFINITIONS: 





INTERIOR
ANGLES 


The
angles between the parallel lines. 











Angles B,
C, E, and H are Interior Angles. 





EXTERIOR
ANGLES 


The
angles NOT between the parallel lines 











Angles A,
D, F, and G are exterior angles. 





CORRESPONDING
ANGLES 


Angles in
the same place on each cross. 











ALTERNATE 


Means one
angle on each side of the crossing line, so: 





ALTERNATE
INTERIOR ANGLES 











ALTERNATE
EXTERIOR ANGLES 











copyright 2005 Bruce Kirkpatrick 
