Question

lines are parallel if they dont intersact proof

Answer 1

there's no proof bcoz the definition of parallels itself says , "if 2 lines don't intersect even on producing on both sides indefinitely , they are parallel."

Hope you understood my friend......

Answer 2

Take a quadrilateral ABCD.

Draw a diagonal AC in Quadrilateral ABCD.,

Now in ∆ ACB and ∆ADB,

AC= BD
AC= AC. Common.
CD=AB.


∆ ACB =~ ∆ ADB.


Since, AC|| BD, AB|| CD. [ corresponding angle]


Since, it is proved that parallel lines need not to intersect.