底数相同的对数相加减，底数不变，增数相乘除。
log12.5-log5/8+log1/2
=log[12.5÷5/8×1/2]
=log[100/8×8/5×1/2]
=log10
=1
10为底
log(12.5) -log(5/8) +log(1/2)
=log(100/8) -log(5/8) +log(1/2)
=log[(100/8)(8/5)(1/2) ]
=log10
=1
lg(12.5/(5/8)*(1/2))
=lg(12.5*8/(5*2))
=lg(2.5*8/2)
=lg10
=1
这是以谁为底呀？
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