# Parallel straight lines

Which are the parallel lines?

I prove that $a$ and $b$ are parallel but can't prove that $c$ and $d$ are parallel. The angles, which are $135^o$ and $45^o$ are alternate angles.They aren't equal , so $c$ isn't parallel to $d$ but the answer is that $c$ is parallel to $d$. Am I right that they aren't?

Edit: They are a little inclined like these:

• To put it simply, yes. If the answer is that they are parallel, I suspect there is more to this than your description allows. – Brandon Carter Nov 14 '10 at 9:09
• Moreover, if the angles are how you say they are, then $C$ and $D$ are perpendicular... – Brandon Carter Nov 14 '10 at 9:10
• Have you tried making an accurate drawing? – J. M. isn't a mathematician Nov 14 '10 at 9:14
• @Carter , they aren't perpendicular.My drawing is wrong. – randomwebdev Nov 14 '10 at 9:15
• Note that $135+45=180$. – Yuval Filmus Nov 14 '10 at 10:03