题目
1 利用导数定义推出:(1)(z^n)'=nz^n-1(n为正整数);(2)((1)/(z))'=-(1)/(z^2).
1 利用导数定义推出:
(1)$(z^{n})'=nz^{n-1}(n$为正整数);
(2)$(\frac{1}{z})'=-\frac{1}{z^{2}}$.
题目解答
答案
(1) 由导数定义,
$(z^n)' = \lim_{h \to 0} \frac{(z+h)^n - z^n}{h}$
展开 $(z+h)^n$ 得
$(z+h)^n = z^n + nz^{n-1}h + \cdots + h^n$
故
$(z^n)' = \lim_{h \to 0} \frac{nz^{n-1}h + \cdots}{h} = nz^{n-1}$
答案: $(z^n)' = nz^{n-1}$
(2) 由导数定义,
$\left(\frac{1}{z}\right)' = \lim_{h \to 0} \frac{\frac{1}{z+h} - \frac{1}{z}}{h} = \lim_{h \to 0} \frac{-h}{z(z+h)h} = -\frac{1}{z^2}$
答案: $\left(\frac{1}{z}\right)' = -\frac{1}{z^2}$
$\boxed{\begin{array}{cc}\text{(1) } (z^n)' = nz^{n-1} \\\text{(2) } \left(\frac{1}{z}\right)' = -\frac{1}{z^2}\end{array}}$