如图,在梯形ABCD中,AD平行于BC,∠BAC=90度,AB=AC,BD=BC,BC,AC,BD相交...答:证明:作高AE,DF,显然AE=DF,在等腰直角三角形ABC中,AE=BC/2,所以DF=BC/2,所以直角三角形BDF中,DF=BC/2=BD,所以∠DBC=30,所以∠BDC=75,∠ACD=∠BCD-∠ACB=75-45=30,∠DOC=75,所以OC=CD 参考资料:http://hi.baidu.com/%CC%D5%D3%C0%C7%E5/blog/item/3db83af1567e4fcf7831aa2a...