# Triangles and parallel lines problem

1. Sep 8, 2014

### lingping7

The picture has the problem and my attempts, I need guidance.

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2. Sep 8, 2014

### HallsofIvy

Staff Emeritus
Okay, you are given that angle 1 is congruent to angle 4 and angle 2 is congruent to angle 3 (you should say that in the proof). Angle 1 is congruent to angle 2 by "VOA" (vertical angles) so all of angles 1, 2, 3, and 4 are congruent to one another. To prove that AC is parallel to BD, you need to show that angle 4 is congruent to angle 6 or that angle 5 is congruent to angle 3 (alternate interior angles).

3. Sep 8, 2014

### lingping7

Yes that is true, I'm able to get angle 5 = to angle 6, but can't equate either of these angles to angle 1,2,3,4

4. Sep 8, 2014

### ArcanaNoir

How can you express the measure of angle 3? Can you express the measure of angle 5 in the same way?
 I think I was transposing the 4 and the 6. >_<

Last edited: Sep 8, 2014
5. Sep 8, 2014

### lingping7

Angle 3 = 180-angle6-angle2
Angle 5 = 180-angle4-angle1
I could say Angle 5 = 180-angle2-angle2
I still don't get it :(