In a plane, if a line is perpendicular to one of two parallel lines, then it is perpendicular to the other line also.
Given:
Prove:
Proof
Statement 
Reason 

1 
Given 

2 
is a right angle 
Definition of perpendicular lines 
3 
Definition of right angle 

4 
Corresponding angles 

5 
Definition of congruent angles 

6 
Substitution Property 

7 
is a right angle 
Definition of right angle 
8 
Definition of perpendicular lines 