I have a geometry question. In this question, We have a Equilateral triangle ($ \triangle BDC$) that we draw it with one point on the circle and 2 point on the diameter. We want to prove if we draw this triangle then $OC = OD$.
I try to prove it But I can't find any good way to prove that. It must solve with central and inscribed angles. Is it possible to help me to solve it?
I'm sorry for bad English.