Note: the published solution considers two possible cases; however, we are recognizing those solvers who considered only one of those cases.
At any point in time Chris is equidistant from Alan and Brianna who are always somewhere on the same straight road. This would create an isosceles triangle at any instant. Let the road for Alan and Brianna be the x-axis (east and west) – it follows that Chris, C, would always be located along a perpendicular bisector “north or south” of the midpoint P between A and B.
Relative to midpoint P Chris must move only vertically in the y-direction so that the points A, B, and C always form an isosceles triangle with the base along the x-axis.
Assume that Alan is moving to the right in the positive x-direction. Because the problem does not specify that Alan and Brianna...