取对数
15a*lg3 =5b*lg5=3c*lg5+3c*lg3
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(15a-3c)lg3=3c lg5
3c lg3= (5b-3c)lg5
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略
取对数
15a*lg3 =5b*lg5=3c*lg5+3c*lg3
--------------------------------
(15a-3c)lg3=3c lg5
3c lg3= (5b-3c)lg5
---------------------------
略