某间接测量量的测量公式为：f = x + y - 2z，则间接测量量f的不确定度合成公式，推导过程正确的是()A. (partial f)/(partial x) = 1，(partial f)/(partial y) = 1，(partial f)/(partial z) = -2，U_f = sqrt(((partial f)/(partial x) U_x)^2 + ((partial f)/(partial y) U_y)^2 + ((partial f)/(partial z) U_z)^2) = sqrt(U_x^2 + U_y^2 + 4U_z^2)B. (partial f)/(partial x) = 1，(partial f)/(partial y) = 1，(partial f)/(partial z) = -1，U_f = sqrt(((partial f)/(partial x) U_x)^2 + ((partial f)/(partial y) U_y)^2 + ((partial f)/(partial z) U_z)^2) = sqrt(U_x^2 + U_y^2 + U_z^2)

本题考查间接测量量不确定度合成公式的推导，解题思路是先根据测量公式求出各直接测量量对间接测量量的偏导数，再代入不确定度传播公式进行计算。

1. 求各偏导数：
   • 对于函数$f = x + y - 2z$，求$\frac{\partial f}{\partial x}$时，将$y$和$z$看作常数，根据求导公式$(X^n)^\prime=nX^{n - 1}$，常数的导数为$0$，可得$\frac{\partial f}{\partial x}=\frac{\partial (x + y - 2z)}{\partial x}=\frac{\partial x}{\partial x}+\frac{\partial y}{\partial x}-\frac{\partial (2z)}{\partial x}=1 + 0 - 0 = 1$。
   • 求$\frac{\partial f}{\partial y}$时，将$x$和$z$看作常数，同理可得$\frac{\partial f}{\partial y}=\frac{\partial (x + y - 2z)}{\partial y}=\frac{\partial x}{\partial y}+\frac{\partial y}{\partial y}-\frac{\partial (2z)}{\partial y}=0 + 1 - 0 = 1$。
   • 求$\frac{\partial f}{\partial z}$时，将$x$和$y$看作常数，可得$\frac{\partial f}{\partial z}=\frac{\partial (x + y - 2z)}{\partial z}=\frac{\partial x}{\partial z}+\frac{\partial y}{\partial z}-\frac{\partial (2z)}{\partial z}=0 + 0 - 2=-2$。
2. 代入不确定度传播公式：
   不确定度传播公式为$U_f = \sqrt{(\frac{\partial f}{\partial x} U_x)^2 + (\frac{\partial f}{\partial y} U_y)^2 + (\frac{\partial f}{\partial z} U_z)^2}$，将$\frac{\partial f}{\partial x} = 1$，$\frac{\partial f}{\partial y} = 1$，$\frac{\partial f}{\partial z} = -2$代入可得：
   $U_f = \sqrt{(1\times U_x)^2 + (1\times U_y)^2 + (-2\times U_z)^2}=\sqrt{U_x^2 + U_y^2 + 4U_z^2}$。
   选项B中$\frac{\partial f}{\partial z} = -1$错误。