Advanced Geometric Problem & Solution (Twice a week update) Now 4666 problems posted.
<Cir-2025-786>, hint
Let <AO'B=2x, <BAD=y then <CBD=x+y
Since AO'DB are conclic , (S'''), <O'AC+<O'DC=180---><O'AC+<O'DA+<ADB+<BDC=180
90-x+(90-x-y)+x +<BDC=180 Thus <BDC=x+y.
Hence <DBC=<BDC, CB=CD
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