In two triangles, when passing through B and B 1 respectively, be/= CD, B1E1= C1D1.

Connect CE, C 1E 1

Construct two congruent triangles.

The title clearly tells you the conditions of congruence.

Congruent triangles can be constructed according to the known conditions of the topic.

In this way, many equal conditions can be deduced.

AE=A 1E 1, 2 congruent quadrilaterals.

Several corners. . . .

be easy to

The idea of drawing is natural and smooth.