Parallel lines are like train tracks.
They never cross.
Parallel Line Theorems
Two parallel lines on their own
are not vary interesting to us
in terms of geometry.
But if straight line (called a
transversal) intersects two
parallel lines, then the
angles created are very
interesting to us…..
These lines are parallel because they will never cross….
The dashed line is called a transversal, because it crosses both lines
As soon as the transversal is drawn, a collection of angles are created.
These angles are equal because of OAT. Copy these to your sheet.
x
y
x
y
x
y
y x
In this diagram, there is a collection of
patterns that can be generated.
y
y
“Z” pattern (alternate angles: AA)
x
x
“Z” pattern
y
x
x
y
“F” pattern (corresponding angles: CA)
x
y
x
y
“F” pattern
y
x
X + Y = 180O
x
y
“C” pattern (supplementary angles: SA)
( also called interior angles )
Find X,Y and Z
70O
Z
Y
X
Statement Reason
Z = 70O
Y = 180O – 70O
=
110O
X = 110O
OAT
SA
OAT
HOMEWORK
see sheet