延长AD到点E,使DE=AD=6,连接CE∵BD=CD,AD=DE,∠ADB=∠CDE∴△ABD≌△CED∴CE=AB=5∵AE=12,CE=5,AC=13∴CE²+AE²=AC²∴∠E=90°∴CD²=5²+6²=61∴CD=√61∴BC=2√61...