As shown in the figure, in the quadrilateral ABCD, AB⊥BC, CD⊥BC and E are points on BC, AB = Ce, and CD = Be.

1. Know the triangle from the condition.

ECD congruence

Therefore, the angle AED= 180- (angle DEC+ angle AEB)=90 degrees.

2.AE=DE

Aide is

Isosceles right triangle

So m is the midpoint of AD.

So BM=CM

EM vertical DM

DMEC

Four dots * * * circle

So the angle MCB=45 degrees

It can be seen from the above that △BCM is an equilateral triangle.

3.△MBC= where is line× BC/2。

Quadrilateral ABCD= there is a straight line in it ×BC.

So it's a general relationship.