题目
设 u = xy + (y)/(x)，则 u_(xx) = ( )A. y - (y)/(x^2)B. -(2y)/(x^3)C. (y)/(x^2) - yD. (2y)/(x^3)
设 $u = xy + \frac{y}{x}$，则 $u_{xx} = (\quad)$
A. $y - \frac{y}{x^2}$
B. $-\frac{2y}{x^3}$
C. $\frac{y}{x^2} - y$
D. $\frac{2y}{x^3}$
题目解答
答案
D. $\frac{2y}{x^3}$