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解:log2(25)=log2(5²)=2log2(5)=2lg5/lg2=2lg(10/2)/lg2=2(1-lg2)/lg2=2(1-a)/a
lg2=a,log(2,25)=log(2,100÷4)=log(2,100)-log(2,4)=2log(2,10)-2=2(lg10/lg2)-2=2/a-2