3'5 Proving Lines Parallel

1
3.5 Proving Lines Parallel
2

• Post 3.5 Given a line a pt not on line,
  theres exactly 1 line thru pt parallel to the
  line

3
Ways to Prove Lines Parallel

• Post 3.4 If 2 lines cut by trans corr angles
  congruent, then lines parallel.
• Thm 3.5 If 2 lines cut by trans alt ext
  angles congruent, then lines parallel.

4
Ways to Prove Lines Parallel

• Thm 3.6 If 2 lines cut by trans cons int
  angles supp, then lines parallel.
• Thm 3.7 If 2 lines cut by trans alt int
  angles congruent, then lines parallel.

5
Ways to Prove Lines Parallel

• Thm 3.8 If 2 lines perpendicular to same line,
  then theyre parallel.

6
Example

• Determine which lines are parallel
• a
• b
• c

103
77
100
7
Example

• Find x ZYN so that PQ .

W
11x - 25
P
Q
X
Y
M
N
7x 35
Z
8
Proof Example
l
m

• Given r s
• 5 6
• Prove l m

6
s
4
7
5
r
statements
reasons
9

• 3.5 p. 155
• (13-31 all, 34-42 even, 48-64 even)