题目
设f(z)=2x(1-y)+i(x²-y²+2y),问函数f(z)在何处可导,并在可导处求出f'(z).
设f(z)=2x(1-y)+i(x²-y²+2y),问函数f(z)在何处可导,并在可导处求出f'(z).
题目解答
答案
将函数 $ f(z) = 2x(1-y) + i(x^2 - y^2 + 2y) $ 分解为实部 $ u(x,y) = 2x(1-y) $ 和虚部 $ v(x,y) = x^2 - y^2 + 2y $。计算偏导数:
\[
\frac{\partial u}{\partial x} = 2 - 2y, \quad \frac{\partial u}{\partial y} = -2x, \quad \frac{\partial v}{\partial x} = 2x, \quad \frac{\partial v}{\partial y} = 2 - 2y
\]
满足柯西-黎曼方程:
\[
\frac{\partial u}{\partial x} = \frac{\partial v}{\partial y}, \quad \frac{\partial u}{\partial y} = -\frac{\partial v}{\partial x}
\]
故函数在复平面上处处可导。导数为:
\[
f'(z) = \frac{\partial u}{\partial x} + i\frac{\partial v}{\partial x} = (2 - 2y) + i(2x)
\]
或表示为:
\[
\boxed{(2 - 2y) + i(2x)} \quad \text{或} \quad \boxed{2 + 2i\overline{z}}
\]