若f‘’(x)存在求函数y=|n[f(x)的二阶导数d^2y分之dx^2

如题所述

ln(y)=f(x)
两边同时求导:
(1/y)*y'=f'(x)
y'=f'(x)*y
y'=e^f(x)*f'(x)
d^2y/dx^2=y''=e^f(x)*f'(x)*f'(x)+e^f(x)*f''(x)=e^f(x)*[(f'(x))^2+f''(x)]
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