题目
设 z = sqrt(x^2) + sqrt(y^2)，则 dz 等于:A. (dx^2 + dy^2)/(2sqrt(x^2) + 2sqrt(y^2))B. (x dx + y dy)/(sqrt(x^2) + sqrt(y^2))C. (dx + dy)/(sqrt(x^2) + sqrt(y^2))D. (x + y)/(sqrt(x^2) + sqrt(y^2)) (dx + dy)
设 $z = \sqrt{x^2} + \sqrt{y^2}$，则 $dz$ 等于:
A. $\frac{dx^2 + dy^2}{2\sqrt{x^2} + 2\sqrt{y^2}}$
B. $\frac{x dx + y dy}{\sqrt{x^2} + \sqrt{y^2}}$
C. $\frac{dx + dy}{\sqrt{x^2} + \sqrt{y^2}}$
D. $\frac{x + y}{\sqrt{x^2} + \sqrt{y^2}} (dx + dy)$
题目解答
答案
B. $\frac{x dx + y dy}{\sqrt{x^2} + \sqrt{y^2}}$