(3) How to determine the position of G-point is the difficulty and focus of this topic.

Let the speed of P on AG be A, then what is the time for P to get from M to A? At least, what is it? Mg+Ag is the smallest, and the vertical intersection P is BM, which crosses BM at E. According to the topic, △ABM is a regular triangle, ∠ BMO = 30 degrees, so PE =? MP？ . To minimize Mg+Ag, minimize AP+PE. According to the shortest line segment between two points, we can deduce that when A, P and E are on a straight line, AP+PE is the smallest, and PE is perpendicular to BM at this time, and P is the point G found at this time.

See the figure below for the process.