help with a proof?

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Question

help with a proof?

http://prntscr.com/57iorq

directrix · Answer

This is a proof of the theorem: In a plane, if  a line is perpendicular to one of two parallel lines, then it is perpendicular to the other one also.

anonymous · Answer

oh, but i need answers, so can you help me?

anonymous · Answer

i got 

1. C
2. B
3. D
4. ?
5. ?

directrix · Answer

What do you think is the reason for statement 2. See attachment.

anonymous · Answer

@Directrix  isnt statement 2 also given?

directrix · Answer

Reason 2 is not given but it is the direct result of what was given. 
What does it mean about angles formed if two lines are perpendicular?
Look at the answer options.

directrix · Answer

What does it mean for two lines to be perpendicular?

directrix · Answer

Think about the definition of perpendicular lines: two lines in a plane that meet to form right angles. So that gives us. See attachment.

directrix · Answer

Yours  @vexus                  Mine

i got 1. C                            1.  B
 2. B                                    2. A
 3. D  Correct                       3. D
 4. ?                                      4.  This is what you want to prove, the "To Prove"
5. ?                                        5.  ?