we know that the point p on the line y=5x that is closest to the point (78 0) will be on the line perpendicular to the line y=5x and go through the point (78 0)
step 1 find the slope m perpendicular to the line y=5x m1=5 if two lines are perpendicular m1*m2=-1 m2=-1/5
step 2 with m=-1/5 and the point (78,0) find the equation of a line y-y1=m*(x-x1)-----> y-0=(-1/5)*(x-78)----> y=-0.20x+15.6
step 3 resolve the equation systems y=5x y=-0.20x+15.6
