设f''(x)存在,求下列函数的二阶导数d^2y/dx^21.y=f(x) 2.y=ln[f(x)]

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设f''''(x)存在,求下列函数的二阶导数d^2y/dx^21.y=f(x)2.y=ln[f(x)]设f''''(x)存在,求下列函数的二阶导数d^2y/dx^21.y=f(x)2.y=ln[f(x)]设f

设f''(x)存在,求下列函数的二阶导数d^2y/dx^21.y=f(x) 2.y=ln[f(x)]
设f''(x)存在,求下列函数的二阶导数d^2y/dx^2
1.y=f(x) 2.y=ln[f(x)]

设f''(x)存在,求下列函数的二阶导数d^2y/dx^21.y=f(x) 2.y=ln[f(x)]
(1)
y=f(x)
d^2y/dx^2
=d(f'(x))/dx
=f''(x)
(2)
y=ln[f(x)]
dy/dx
=f'(x)/f(x)
d^2y/dx^2
=d[f'(x)/f(x)]/dx
=[f''(x)f(x)-f'(x)f'(x)]/f^2(x)
=(f''(x)f(x)-[f'(x)]^2)/f^2(x)