There is a square ABCD whose side length is Q. P is a point on the diagonal BD. when p is at what position, the value of AP + BP + CP is the minimum

There is a square ABCD whose side length is Q. P is a point on the diagonal BD. when p is at what position, the value of AP + BP + CP is the minimum

The minimum value is not 3 / 2 √ 2q, because we can find a smaller value: when P and B coincide, AP + BP + CP = 2q. To find the minimum value of L = AP + BP + CP, we can use the method of analytic geometry