hmmm to tell if they're orthogonal(perpendicular) to each other, we can simply get their dot-product, if their dot-product is 0, then they indeed are perpendicular, let's check
[tex]\bf \ \textless \ 7,-4\ \textgreater \ \cdot \ \textless \ -28,16\ \textgreater \ \implies (7\cdot -28)+(-4\cdot 16)\implies -190[/tex]
well, no luck there... now, let's introspect the digits a little
[tex]\bf \begin{array}{llll}
\ \textless \ 7,-4\ \textgreater \ \qquad \ \textless \ &-28,&16\ \textgreater \ \\
&~~\uparrow &~\uparrow \\
&-4\cdot 7&-4\cdot -4
\end{array}[/tex]
notice, the second vector, -28, 16, is just a multiple of the first one, that simply means, they're parallel.
you can always just do a b/a check and simplify both vectors, if they yield the same ratio, they're parallel, since they're just multiples of each other.
