When BM is minimum, the coordinate of m is M(x 1, y 1).

Then x 1=20, y 1→0, BM→0.

When BN is the minimum, the coordinate of n is N(x2, y2).

Then x2→20, y2=0, BM→0.

At this time, BM→0, MN→0 and BM+MN→0 are the minimum values.

∴ When BM is minimum, the coordinates of m are M(x 1, y 1), x 1=20, y 1→0.

When the moving point m, n can be at the vertex position of ABCD, then

The coordinate of m is m (20 20,0),