They look like two zeros, no matter how far or close. they are indispensable for some people, but useless for other people. what are they?

300

step-by-step explanation:

28-600w < 300

28-600w > 300

600-28w < 300

600-28w > 300

step-by-step explanation:

points a and b are equidistant from the desired line, so the line you find by using them will go through point r.

using points other than a and b will give the desired line only if they are equidistant from r. if they are randomly located, the perpendicular line you create will not necessarily go through point r, hence will not be a solution to the problem.