dear meritnation experts,

plz provide me with the proof for theorem 5.1 -

which states the two distinct lines cannot more than one point in common.

i didn't understood it....plzzzzzhelp me out as soon as posssible.

 Yes, it is true. 

Two distinct lines do not have more than one point in common.

They have given two distinct lines which are not parallel. They may be perpendicular or intersecting. Let two lines be a and b

In perpendicular lines a perpendiclar to b meets at a point. 

In intersecting lines they meet at a point. So from these two cases you can conclude that 2 lines cannot have more than one point in common