设有两个函数：
$y_1 = u(x) ，y_2 = v(x)$
①$(u \pm v)’ = u’ \pm v’$
② $(u \cdot v)’ = u’v + uv’$
推广：$(u \cdot v \cdot w)’ = u’vw + uv’w + uvw’$
③ $\left( \frac{v}{u} \right)’ = \frac{v’u - vu’}{u^2}$
记：$\left( \frac{子}{母} \right)’ = \frac{子’母 - 子母’}{母^2}$

$eg ： y = k \cdot u ， k 为常数，则 y’ = k \cdot u’ (k \cdot u)’ = k \cdot u’$

(奇)’=偶；(偶)’=奇，⇒求导改变奇偶性。

基础符号认识
① $f’(x) \Rightarrow f(x)$的一阶导数 $y’ = \frac{dy}{dx} = f’(x)$
② $f’’(x) \Rightarrow f(x)$的二阶导数，$y’’ = \frac{d^2y}{dx^2}$
③ 对$y = f(x)$，求$n$次导数$\Rightarrow$：$f^{(n)}(x) = \frac{d^ny}{dx^n}$
④ 具体一个点$x_0$处的导数：$f’(x_0) = \frac{dy}{dx}\big|{x = x_0}$
$f’’(x_0) = \frac{d^2y}{dx^2}\big|{x = x_0}$