设y＝f（lnx）/x，其中f二阶可导，求y''

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如春薯乱辩图扒陪者

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y= f(lnx)/x
y'让渗谨塌 = [f'(lnx) - f(lnx) ]/x^2
y'坦晌脊'
= -2[f'(lnx) - f(lnx) ]/x^3 + (1/x^2) .[ (1/x) f''(lnx) - (1/x)f'(lnx) ]
= { -2[f'(lnx) - f(lnx) ] + f''(lnx) - f'(lnx) }/x^3
= [ f''(lnx) -3f'(lnx) +2f(lnx)]/x^3

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