4. 微分
4.3 导数四则运算与反函数求导法则
双曲正弦函数 sh x = e x − e − x 2 \sh x=\frac{e^x-e^{-x}}{2} shx=2ex−e−x
双曲余弦函数 ch x = e x + e − x 2 \ch x=\frac{e^x+e^{-x}}{2} chx=2ex+e−x
ch 2 x − sh 2 x = 1 \ch^2 x-\sh^2 x=1 ch2x−sh2x=1
( e − x ) ′ = ( 1 e x ) ′ = − e x e 2 x = − e − x (e^{-x})'=(\frac{1}{e^x})'=-\frac{e^x}{e^{2x}}=-e^{-x} (e−x)′=(ex1)′=−e2xex=−e−x
( sh x ) ′ = 1 2 ( e x + e − x = ch x ) (\sh x)'=\frac{1}{2}(e^x+e^{-x}=\ch x) (shx)′=21(ex+e−x=chx)
同理 ( ch x ) ′ = sh x (\ch x)' = \sh x (chx)′=shx
双曲正切函数 th x = sh x ch x \th x=\frac{\sh x}{\ch x} thx=chxshx
双曲余切函数 cth x = ch x sh x \cth x=\frac{\ch x}{\sh x} cthx=shxchx
( th x ) ′ = ch 2 x − sh 2 x ch 2 x = 1 ch 2 x = sech 2 x (\th x)'=\frac{\ch^2 x-\sh^2 x}{\ch^2 x}=\frac{1}{\ch^2 x}=\text{sech}^2 x (thx)′=ch2xch2x−sh2x=ch2x1=sech2x
同理 ( cth x ) ′ = csch 2 x (\cth x)'=\text{csch}^2 x (cthx)′=csch2x
( sh − 1 x ) = 1 ( sh y ) ′ = 1 ch y = 1 1 + sh 2 y = 1 1 + x 2 (\sh^{-1} x)=\frac{1}{(\sh y)'}=\frac{1}{\ch y}=\frac{1}{\sqrt{1+\sh ^2 y}}=\frac{1}{\sqrt{1+x^2}} (sh−1x)=(shy)′1=chy1=1+sh2y1=1+x21
同理 ( ch − 1 x ) ′ = 1 x 2 − 1 (\ch^{-1} x)'=\frac{1}{\sqrt{x^2-1}} (ch−1x)′=x2−11
( th − 1 x ) ′ = ( cth − 1 x ) = 1 1 − x 2 (\th^{-1} x)'=(\cth^{-1} x)=\frac{1}{1-x^2} (th−1x)′=(cth−1x)=1−x21
4.3.3 基本初等函数的导数公式
( C ) ′ = 0 d ( C ) = 0 ⋅ d x = 0 ( x α ) ′ = α x α − 1 d ( x α ) = α x α − 1 d x ( sin x ) ′ = cos x d ( sin x ) = cos x d x ( cos x ) ′ = − sin x d ( cos x ) = − sin x d x ( tan x ) ′ = sec 2 x d ( tan x ) = sec 2 x d x ( cot x ) ′ = − csc 2 x d ( cot x ) = − csc 2 x d x ( sec x ) ′ = tan x sec x d ( sec x ) = tan x sec x d x ( csc x ) ′ = − cot x csc x d ( csc x ) = − cot x csc x d x ( arcsin x ) ′ = 1 1 − x 2 d ( arcsin x ) = d x 1 − x 2 ( arccos x ) ′ = − 1 1 − x 2 d ( arccos x ) = − d x 1 − x 2 ( arctan x ) ′ = 1 1 + x 2 ( arccot x ) ′ = − 1 1 + x 2 ( a x ) ′ = ln a ⋅ a x 特别地 ( e x ) ′ = e x ( log a x ) ′ = 1 ln a ⋅ 1 x 特别地 ( ln x ) ′ = 1 x ( sh x ) ′ = ch x ( ch x ) ′ = sh x ( th x ) ′ = sech 2 x ( cth x ) ′ = − csch 2 x ( sh − 1 x ) ′ = 1 1 + x 2 ( ch − 1 x ) ′ = 1 x 2 − 1 d ( arctan x ) = d x 1 + x 2 ( th − 1 x ) ′ = ( cth − 1 x ) ′ = 1 1 − x 2 d ( arccot x ) = − d x 1 + x 2 d ( a x ) = ln a ⋅ a x d x 特别地 d ( e x ) = e x d x d ( log a x ) = 1 ln a ⋅ d x x 特别地 d ( ln x ) = d x x d ( sh x ) = ch x d x d ( ch x ) = sh x d x d ( th x ) = sech 2 x d x d ( cth x ) = − csch 2 x d x d ( sh − 1 x ) = d x 1 + x 2 d ( ch − 1 x ) = d x x 2 − 1 d ( th − 1 x ) = d ( cth − 1 x ) = d x 1 − x 2 \begin{array}{l} (C)^{\prime}=0 \\ \mathrm{~d}(C)=0 \cdot \mathrm{~d} x=0 \\ \left(x^{\alpha}\right)^{\prime}=\alpha x^{\alpha-1} \\ \mathrm{~d}\left(x^{\alpha}\right)=\alpha x^{\alpha-1} \mathrm{~d} x \\ (\sin x)^{\prime}=\cos x \\ \mathrm{~d}(\sin x)=\cos x \mathrm{~d} x \\ (\cos x)^{\prime}=-\sin x \\ \mathrm{~d}(\cos x)=-\sin x \mathrm{~d} x \\ (\tan x)^{\prime}=\sec ^{2} x \\ \mathrm{~d}(\tan x)=\sec ^{2} x \mathrm{~d} x \\ (\cot x)^{\prime}=-\csc ^{2} x \\ \mathrm{~d}(\cot x)=-\csc ^{2} x \mathrm{~d} x \\ (\sec x)^{\prime}=\tan x \sec x \\ \mathrm{~d}(\sec x)=\tan x \sec x \mathrm{~d} x \\ (\csc x)^{\prime}=-\cot x \csc x \\ \mathrm{~d}(\csc x)=-\cot x \csc x \mathrm{~d} x \\ (\arcsin x)^{\prime}=\frac{1}{\sqrt{1-x^{2}}} \\ \mathrm{~d}(\arcsin x)=\frac{\mathrm{d} x}{\sqrt{1-x^{2}}} \\ (\arccos x)^{\prime}=-\frac{1}{\sqrt{1-x^{2}}} \quad \mathrm{~d}(\arccos x)=-\frac{\mathrm{d} x}{\sqrt{1-x^{2}}} \\ (\arctan x)^{\prime}=\frac{1}{1+x^{2}} \\ (\operatorname{arccot} x)^{\prime}=-\frac{1}{1+x^{2}} \\ \left(a^{x}\right)^{\prime}=\ln a \cdot a^{x} \\ \text { 特别地 }\left(e^{x}\right)^{\prime}=e^{x} \\ \left(\log _{a} x\right)^{\prime}=\frac{1}{\ln a} \cdot \frac{1}{x} \\ \text { 特别地 }(\ln x)^{\prime}=\frac{1}{x} \\ (\operatorname{sh} x)^{\prime}=\operatorname{ch} x \\ (\operatorname{ch} x)^{\prime}=\operatorname{sh} x \\ (\text { th } x)^{\prime}=\operatorname{sech}^{2} x \\ (\operatorname{cth} x)^{\prime}=-\operatorname{csch}^{2} x \\ \left(\operatorname{sh}^{-1} x\right)^{\prime}=\frac{1}{\sqrt{1+x^{2}}} \\ \left(\operatorname{ch}^{-1} x\right)^{\prime}=\frac{1}{\sqrt{x^{2}-1}} \\ \mathrm{~d}(\arctan x)=\frac{\mathrm{d} x}{1+x^{2}} \\ \left(\operatorname{th}^{-1} x\right)^{\prime}=\left(\operatorname{cth}^{-1} x\right)^{\prime}=\frac{1}{1-x^{2}} \\ \mathrm{~d}(\operatorname{arccot} x)=-\frac{\mathrm{d} x}{1+x^{2}} \\ \mathrm{~d}\left(a^{x}\right)=\ln a \cdot a^{x} \mathrm{~d} x \\ \text { 特别地 } d\left(e^{x}\right)=e^{x} d x \\ \mathrm{~d}\left(\log _{a} x\right)=\frac{1}{\ln a} \cdot \frac{\mathrm{~d} x}{x} \\ \text { 特别地 } \mathrm{d}(\ln x)=\frac{\mathrm{d} x}{x} \\ \mathrm{~d}(\operatorname{sh} x)=\operatorname{ch} x \mathrm{~d} x \\ \mathrm{~d}(\operatorname{ch} x)=\operatorname{sh} x \mathrm{~d} x \\ \mathrm{~d}(\text { th } x)=\operatorname{sech}^{2} x \mathrm{~d} x \\ \mathrm{~d}(\operatorname{cth} x)=-\operatorname{csch}^{2} x \mathrm{~d} x \\ \mathrm{~d}\left(\operatorname{sh}^{-1} x\right)=\frac{\mathrm{d} x}{\sqrt{1+x^{2}}} \\ \mathrm{~d}\left(\operatorname{ch}^{-1} x\right)=\frac{\mathrm{d} x}{\sqrt{x^{2}-1}} \\ \mathrm{~d}\left(\operatorname{th}^{-1} x\right)=\mathrm{d}\left(\operatorname{cth}^{-1} x\right)=\frac{\mathrm{d} x}{1-x^{2}} \end{array} (C)′=0 d(C)=0⋅ dx=0(xα)′=αxα−1 d(xα)=αxα−1 dx(sinx)′=cosx d(sinx)=cosx dx(cosx)′=−sinx d(cosx)=−sinx dx(tanx)′=sec2x d(tanx)=sec2x dx(cotx)′=−csc2x d(cotx)=−csc2x dx(secx)′=tanxsecx d(secx)=tanxsecx dx(cscx)′=−cotxcscx d(cscx)=−cotxcscx dx(arcsinx)′=1−x21 d(arcsinx)=1−x2dx(arccosx)′=−1−x21 d(arccosx)=−1−x2dx(arctanx)′=1+x21(arccotx)′=−1+x21(ax)′=lna⋅ax 特别地 (ex)′=ex(logax)′=lna1⋅x1 特别地 (lnx)′=x1(shx)′=chx(chx)′=shx( th x)′=sech2x(cthx)′=−csch2x(sh−1x)′=1+x21(ch−1x)′=x2−11 d(arctanx)=1+x2dx(th−1x)′=(cth−1x)′=1−x21 d(arccotx)=−1+x2dx d(ax)=lna⋅ax dx 特别地 d(ex)=exdx d(logax)=lna1⋅x dx 特别地 d(lnx)=xdx d(shx)=chx dx d(chx)=shx dx d( th x)=sech2x dx d(cthx)=−csch2x dx d(sh−1x)=1+x2dx d(ch−1x)=x2−1dx d(th−1x)=d(cth−1x)=1−x2dx
【注】(1) [ ∑ i = 1 n c i f i ( x ) ] ′ = ∑ i = 1 n c i f ′ i ( x ) \left[\sum\limits_{i=1}^{n} c_{i} f_{i}(x)\right]^{\prime}=\sum\limits_{i=1}^{n} c_{i} f^{\prime}{ }_{i}(x) [i=1∑ncifi(x)]′=i=1∑ncif′i(x),其中 c i ( i = 1 , 2 , ⋯ , n ) c_{i}(i=1,2, \cdots, n) ci(i=1,2,⋯,n)为常数;
(2) [ ∏ i = 1 n f i ( x ) ] ′ = ∑ j = 1 n { f j ′ ( x ) ∏ i = 1 , i ≠ j n f i ( x ) } \left[\prod\limits_{i=1}^{n} f_{i}(x)\right]^{\prime}=\sum\limits_{j=1}^{n}\left\{f^{\prime}_{j}(x) \prod\limits_{i=1,i\ne j}^{n} f_{i}(x)\right\} [i=1∏nfi(x)]′=j=1∑n{fj′(x)i=1,i=j∏nfi(x)}(每一项是有一个因式的函数求导,其他不求导,然后相乘)
【例4.3.12】 y = a n x n + a n − 1 x n − 1 + . . . + a 1 x + a 0 y=a_nx^n+a_{n-1}x^{n-1}+...+a_1x+a_0 y=anxn+an−1xn−1+...+a1x+a0,求 y ′ y' y′.
【解】 y ′ = n a n x n − 1 + ( n − 1 ) a n − 1 x n − 2 + . . . + a 1 y' = na_nx^{n-1}+(n-1)a_{n-1}x^{n-2}+...+a_1 y′=nanxn−1+(n−1)an−1xn−2+...+a1
【例4.3.13】 y = e x ( x 2 + 3 x − 1 ) arcsin x y=e^x(x^2+3x-1)\arcsin x y=ex(x2+3x−1)arcsinx,求 y ′ y' y′.
【解】 y ′ = e x ( x 2 + 3 x − 1 ) arcsin x + e x ( 2 x + 3 ) arcsin x + e x ( x 2 + 3 x − 1 ) 1 1 − x 2 = e x ( ( x 2 + 5 x + 2 ) arcsin x + x 2 + 3 x − 1 1 − x 2 ) y'=e^x(x^2+3x-1)\arcsin x+ e^x(2x+3)\arcsin x + e^x(x^2+3x-1)\frac{1}{\sqrt{1-x^2}}=e^x((x^2+5x+2)\arcsin x+\frac{x^2+3x-1}{\sqrt{1-x^2}}) y′=ex(x2+3x−1)arcsinx+ex(2x+3)arcsinx+ex(x2+3x−1)1−x21=ex((x2+5x+2)arcsinx+1−x2x2+3x−1)