To require the partial derivative of z to x, we only need to regard y as a constant, that is, z=f(x, y) is a univariate function about x, and then we can find az/ax according to the derivative law of univariate function. Similarly, the same is true for finding the partial derivative of Z to Y. The meaning of the problem is: Z = ln (1UV) = ln (1x 2-y 2), (take the derivative of X, y is regarded as a constant, and the derivative rule of composite function is f' (x) = f' [g (x). ...