如图,在△ABC中,AB=AC,D为BC上任意一点,求证:AD 2 +BD∠DC=AB 2 .

2025-06-25 23:10:19
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回答1:

证明:作AE⊥BC于E,则
AB 2 =AE 2 +BE 2 ,AD 2 =AE 2 +DE 2 ,
则AB 2 -AD 2 =(AE 2 +BE 2 )-(AE 2 +DE 2 )=+BE 2 )-(AE 2 +DE 2 )=(BE+DE)(BE-DE)=BD•DC,
则AD 2 +BD•DC=AB 2 .