You signed in with another tab or window. Reload to refresh your session.You signed out in another tab or window. Reload to refresh your session.You switched accounts on another tab or window. Reload to refresh your session.Dismiss alert
$[ u ( x ) \pm v ( x ) ] ^ { \prime } = u ^ { \prime } ( x ) \pm v ^ { \prime } ( x )$
$( e ^ { x } + 4 \ln x ) ^ { \prime } = ( e ^ { x } ) ^ { \prime } + ( 4 \ln x ) ^ { \prime } = e ^ { x } + \frac { 4 } { x }$
$[ u ( x ) \cdot v ( x ) ] ^ { \prime } = u ^ { \prime } ( x ) \cdot v ( x ) + u ( x ) \cdot v ^ { \prime } ( x )$
$( \sin x \cdot \ln x ) ^ { \prime } = ( \sin x ) ^ { \prime } \cdot \ln x + \sin x \cdot ( \ln x ) ^ { \prime } = \cos x \cdot \ln x + \sin x \cdot \frac { 1 } { x }$
$[ \frac { u ( x ) } { V ( x ) } ] ^ { \prime } = \frac { u ^ { \prime } ( x ) \cdot v ( x ) - u ( x ) \cdot v ^ { \prime } ( x ) } { v ^ { 2 } ( x ) }$
$( \frac { e ^ { x } } { \cos x } ) ^ { \prime } = \frac { ( e ^ { x } ) ^ { \prime } \cdot \cos x - e ^ { x } \cdot ( \cos x ) ^ { \prime } } { \cos ^ { 2 } ( x ) } = \frac { e ^ { x } \cdot \cos x - e ^ { x } \cdot ( - \sin x ) } { \cos ^ { 2 } ( x ) }$
${ g [ h ( x ) ] } ^ { \prime } = g ^ { \prime } ( h ) \cdot h ^ { \prime } ( x )$
$( e ^ { 2 x } ) ^ { \prime } = e ^ { 2 x } \cdot ( 2 x ) ^ { \prime } = 2 e ^ { 2 x } \quad ( \sin 2 x ) ^ { \prime } = \cos 2 x \cdot ( 2 x ) ^ { \prime } = 2 \cos 2 x$
第一节-求极限
一、直接代入型
解题思路:
直接代入
${ (1) }f ( x ) = x ^ { 2 } - \frac { 3 } { x },{ 求 } \lim _ { x \rightarrow 3 } f ( x )$
$$\left. \begin{array} { c } { \text { 解:将 } x = 3 \text { 代入 } f ( x ) = x ^ { 2 } - \frac { 3 } { x } } \ { f ( 3 ) = 3 ^ { 2 } - \frac { 3 } { 3 } = 8 } \ { \therefore \lim _ { x \rightarrow 3 } f ( x ) = 8 } \end{array} \right.$$
${(2)}f ( x ) = \sin x + e ^ { x},{求} \lim _ { x \rightarrow \pi } f ( x )$
$$\left. \begin{array} { c } { \text { 解:将 }x = \pi \text { 代入 } f ( x ) = \sin x + e ^ { x } } \ { f ( \pi ) = \sin \pi + e ^ { \pi } = e ^ { \pi } } \ { \therefore\lim _ { x \rightarrow \pi } f ( x ) = e ^ { \pi } } \end{array} \right.$$
二、$\frac { \infty } { \infty }$型
解题思路:
$$\begin{cases}
分子最高次数大于分母:& \lim _ { x \rightarrow \infty } f ( x ) = \infty\\
分母最高次数大于分子:& \lim _ { x \rightarrow \infty } f ( x ) = 0\\
分子分母最高次数相同:& \lim _ { x \rightarrow \infty } f ( x ) = 分子分母系数比
\end{cases}$$
或者,对分子分母同时求导后再代入,可以多次求导
${(1)已知}f ( x ) = \frac { 7 x ^ { 8 } + x ^ { 6 } + 9 x ^ { 4 } } { 6 x ^ { 5 } + 4 x ^ { 3 } + 2 x } , \lim _ { x \rightarrow \infty } f ( x ) =$