∠∠DEC =∠BCE = 90
∴DEIIMNIIBC
∫M is the midpoint of BD.
∴N is the midpoint of the Chief Executive.
∴MN=(DE+BC)/2
∫△ADE?△BAC
∴AC=DE AE=BC
∴EC=AC+AE=BE+BC
∴NE=NC=EC/2=(BE+BC)/2
∴MN=NE=NC
△ EMC is an isosceles right triangle.
I hope I can help you O(∩_∩)O