设函数y=y(x)由方程xe^f(y)=ln2009e^y确定,其中f具有二阶导数,且f'≠1,则d^2y/dx^2

xe^f(y)=ln2009e^y
e^f(y)+xe^f(y)*f'(y)*y' = y'
e^f(y)(1+xf'y')=y'
e^f*f'*y' (1+xf'y')+e^f(f'y'+xy'f''y'+xf'y'')=y(ln2009e^y)'=(ln2009+lne^y)'=(ln2009+y)'=y'