Question

a straight line through points p and q is drawn perpendicular to a line through points p(x,y) and r(x,(y+10)) . the possible coordinates of the point q are_?

Answer 1

On the X-Y plane, the points p and r are on the vertical line X=x. Then the perpendicular (horizontal) line through p will have the equation Y=y. Points q on that line will have coordinates

... q(<anything>, y)