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问题: 初二数学题

三角形中AD垂直BC于D,BE垂直AC于E,且AD=BC,M是BC中点,AD交BC于H,求证DH+HM=1/2BC

解答:

△ABC中,AD⊥BC于D,BE⊥AC于E,且AD=BC,M是BC中点,AD交BC于H
求证:DH+HM=BC/2

证明:
Rt△BDH∽Rt△ADC--->HD:DC=BD:AD--->HD•AD=BD•DC
令:AD=BC=2BM=2CM=2x
--->HD•2x = (x-DM)(x+DM) = x²-DM²
--->x²-2xHD = DM²
--->x²-2xHD+HD² = DM²+HD²
--->(x-HD)² = MH²
--->x-HD = MH
--->HD+MH = x = BC/2 (证毕)