write a two column proof of theorem 3.12
given m is perpendicular to L and N to L.
Prove: M is parallel to N
write a two column proof of theorem 3.12
given m is perpendicular to L and N to L.
Prove: M is parallel to N
^
|B A
<-------------------|-------.--------> m
|
|
.C
|
<-------------------|-------.--------> n
|D E
|
| L
Statement Reason
line m is perpendicular to line L Given
line n is perpendicular to line L Given
line m makes right angle (angle ABC) to line L Definition of perpendicular lines
line n makes right angle (angle CDE) to line L Definition of perpendicular lines
angle ABC = 90° and angle CDE = 90° Definition of right angle
angle ABC + angle CDE = 180° Addition property of equality
line m is parallel to line n Converse of same side interior angles theoram (if same side interior angles are supplementary, then the lines are parallel)
Using the following diagram with points A,B,C,D marked
L: |
m: A-------------------B---------------------------
|
|
n: ---------------------C--------------------------D
|
Statement | Reason
m and n perpendicular to L | Given.
ABC and DCB are right angles | Definition of perpendicular.
ABC = DCB = 90° | Definition of right angle.
m || n | Alternate interior angle theorem.

Tim H.
Nels B.
Peter D.