如图11-3-43,在△ABC中,AB=AC,AD是BC边上的中线,则AD⊥BC,请说明理由.

如图11-3-43,在△ABC中,AB=AC,AD是BC边上的中线,则AD⊥BC,请说明理由.
如图11-3-44是一个测平架，AB=AC,在BC的中点D挂一个重锤，自然下垂，使用时调整架身，使点A恰好在重锤线上，就说明此时BC处于水平位置，你能说明其中的道理吗？对不起！·······~对不起！·······~对不起！·······~对不起！·······~对不起！·······~对不起！·······~对不起！·······~对不起！·······~对不起！·······~对不起！·······~对不起！·······~对不起！·······~对不起！·······~对不起！·······~对不起！·······~对不起！·······~对不起！·······~对不起！·······~对不起！·······~对不起！·······~对不起！·······~对不起！·······~对不起！·······~对不起！·······~对不起！·······~对对不不起起