In the known isosceles triangle ABC, AB = ACd, E is the midpoint of AB and AC respectively, and CD crosses BE in O, which proves that OB = OC.

Since AB=AC, D and E are the midpoint, there is BD = CE.

The middle angle of the other isosceles triangle ABC = ACB；; ; And BC = BC, then the triangle BCD and BCE are congruent;

Available angle DCB = EBC；; ;

In the triangle OBC, if the two base angles are equal, it is an isosceles triangle, that is, OB = OC.

Complete the certificate!