Imagine that each line could go on forever for example if R and Q kept moving in each direction the lines would eventually touch/cross over one another this would make them intersecting line segments, parallel means never touching so the line segments Q and T would never touch each other making them parallel, the same goes for line segments R and S.
Roster or tabular form: In roster form, all the elements of a set are listed, the elements are being separated by commas and are enclosed within braces { }.
