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问题: 勾股定理~~急急~~

如图,△ABC中,AD⊥BC,AB=9,AC=6,M是AD上任意一点.求MB^2-MC^2

解答:

MB^2-MC^2
=(BD^2+MD^2)-(CD^2+MD^2)
=BD^2-CD^2
=(AB^2-AD^2)-(AC^2-AD^2)
=AB^2-AC^2
=81-36=45