How to do leveling in the second question of the first volume of the eighth grade of junior high school mathematics book, page 34?

Because AB=AC, MB=MC, AM=AM.

So triangle AMB congruent triangles AMC

So the angle MAB equals the angle MAC.

Because AB=AC

So angle ABC is equal to angle ACB.

And prove that triangle AB? With triangular AC? It is proved that there are two congruent angles (AAS) and there is another coincident edge.

So b? =C？ Angle a? B= angle a? C

That would be great. . .

(? It is the midpoint of BC, and there is no book at hand.