1.

It is easy to know that triangle ABC and triangle BDE are congruent triangles, then

Connect CM, ME and EN. Because triangles are congruent, we can see that

NE=CM。

Because of the midpoint of point n, AB=2BC=BD.

So CN = me

So every two opposite sides of the quadrilateral CNEM are equal, so the quadrilateral CNEM is a parallelogram.

While MN and CE are diagonals of a parallelogram, then the diagonals are equally divided, and CK=EK is obtained.

I don't see Figure 3-2. Please look at the picture above.