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问题: 高一数学题

变式引申:已知2^a*3^b=2^c*3^d=6
求证:(a-1)(d-1)=(b-1)(c-1)

解答:

2^a×3^b=6
====> alg2+blg3=lg6....(1)
2^c×3^d=6
====> clg2+dlg3=lg6....(2)
(1)×d-(2)×b ==> (ad-bc)lg2=(d-b)lg6....(3)
(2)×a-(1)×c ===>(ad-bc)lg3=(a-c)lg6....(4)
(3)+(4), 因为lg2+lg3=lg6
===>(ad-bc)=(d-b)+(a-c)
==>ad-a-d=bc-b-c
==>(a-1)(d-1)=(b-1)(c-1)