Because BC is perpendicular to m,
So the angle BMD = 90, so the angle EMC = 90 (equal to the vertex angle).
So angle DEC+ angle BCE=90.
Because angle A = 90, angle ABC+ angle ACB =180-90 = 90.
So angle DEC= angle ABC
So in triangle ABC and triangle CED,
AB = EC
Angle BAC= angle ECD
Angle DEC= angle ABC
So triangle ABC is equal to triangle CED (ASA)
So BC=DE (the corresponding sides of congruent triangles are equal).
With longing and expectation for the national training project, after experiencing the anxiety that the storm plane was delayed, changed and caught th