导数公式的证明最全版.docx
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导数公式的证明最全版
导数的定义:
f(x)=lim刖bx
△x宀0(下面就不再标明△xt了)
用定义求导数公式
(1)f(x)=xAn
证法一:
(n为自然数)
f'(x)
=lim[(x+△-xx)An]/△x
=lim(x+-△x)x[(x+△x)-A1()n+x*(x+△
x)A(n-2)+...+xA(n-2)*(x+△x)+x-A1(n)]/△x
=lim[(x+△x)A-(1n)+x*(x+△x)-A2(n)+...+xA(n-2)*(x+△x)+x-A1(n)]=xA(n-1)+x*xA(n-2)+xA2*xA(n-3)+...xA(n-2)*x+xA(n-1)=nxA(n-1)证法二:
(n为任意实数)
f(x)=xAn
lnf(x)=nlnx
(lnf(x))'=(nlnx)'
f'(x)/f(x)=n/x
f'(x)=n/x*f(x)
f'(x)=n/x*xAn
f(x)二nxA(n-1)
(2)f(x)=sinx
f'(x)
=lim(sin(x+-six)x)/Ax
=lim(sinxcosAx+cosxsinx)/AxXx
=lim(sinx+cosxsin-sinx)/xAx
=limcosxsinAx/Ax
=cosx
(3)f(x)=cosx
f'(x)
=lim(cos(x+-ctos))/Ax
=lim(cosxcos-sinxsin-Acxx)/Ax
=lim(cosx-sinxsin-Aos)/Ax
=lim-sinxsinAx/Ax
=-sinx
(4)f(x)=aAx
证法一:
f'(x)
=lim(aA(x+-aAx)/Ax
=limaAx*(aA-1)/xAx
(设aAA-1=m,贝卩Ax=logaA(m+⑪
=limaAx*m/logaA(m+1)
=limaAx*m/[ln(m+1)/lna]
=limaAx*lna*m/ln(m+1)
=limaAx*lna/[(1/m)*ln(m+1)]
=limaAx*lna/ln[(m+1)A(1/m)]
=limaAx*lna/lne
=aAx*lna
证法二:
f(x)=aAx
lnf(x)=xlna
[lnf(x)]'=[xlna]'
f'(x)/f(x)=lna
f'(x)=f(x)lna
f'(x)=aAxlna
若a=e,原函数f(x)=eAx
则f'(x)=eAx*lne=eAx
(5)f(x)=logaAx
f'(x)
=lim(logaA(x+-logxAx)/Ax
=limlogaA[(x+Ax)/x]/Ax
=limlogaA(1+Ax/x)/Ax
limIn(1+△x/x)/(lna*△x)
limx*ln(1+△x/x)/(x*lna*△x)
lim(x/△x)*ln(1+△x/x)/(x*lna)
=limln[(1+
△x/x)A(x/△x)]/(x*lna)
=limlne/(x*lna)
=1/(x*lna)
若a=e,原函数f(x)=IogeAx=Inx
则f'(x)=1/(x*lne)=1/x
(6)f(x)=tanx
f'(x)
=lim(tan(x+
-△nx)/△x
=lim(sin(x+
△x)/cos(x+nx/abxo/△x
=lim(sin(x+sinxcos△
△x)Coscos(K+△x)/(△xcos(x+△x))=lim(sinxcos△xcosx+sin
x+sinxsin△x)/(△xcos(x+△x))
=limsin△x/(△xcos(x+△x))=1/(cosx)A2=secx/cosx=(secx)A2=1+(tanx)A2(7)f(x)=cotx
f'(x)
=lim(cot(x+
-△tx)/△x
=lim(cos(x+
△x)/sin(xcosx/Anx)/△x
=lim(cos(x+△x)sCosxsin(x+
△x))/(
△xsin(x+
△x))=lim(c
△Wxsinx
cosxsinxcos-△coxsxsin△xcosx)/(△xsin(x+△x))
=lim-sin△x/(△xsin(x+△x))
=-1/(sinx)八2二-cscx/sinx=-(secx)八2=-1-(cotx)八2
(8)f(x)=secx
f'(x)
=lim(sec(x+-△sexc)x)/△x
=lim(1/cos(x+-t/cx$x)/△x
=lim(cosx-cos(x+△x)/(△xcos△x)
△x/(△xcc
=lim(cosx-cosxcos△x+sinxsin△x)/(△xcos(x+△x))=limsinxsin
二sinx/(cosx)A2=tanx*secx
(9)f(x)=cscx
f'(x)
=lim(csc(x+-△csxc)x)/△x
=lim(1/sin(x+-1△/sinxx))/△x
=lim(sinx-sin(x+△x))/(△xsin(x+△x))
△x))
=lim(sinx-sinxcos-△xx△xcosx)/(△xsin(x+-△nx))^Hmosx/(△xsin(x+
=-cosx/(sinx)A2=-cotx*cscx
(10)f(x)=xAx
lnf(x)=xlnx
(lnf(x))'=(xlnx)'
f'(x)/f(x)=lnx+1
f'(x)=(lnx+1)*f(x)
f(x)=(lnx+1)*x^x
(12)h(x)=f(x)g(x)
h'(x)
=lim(f(x+△x)g(xl+x)g(x))/Ax
=lim[(f(x+A(x)+f(x))*g(x+Ax)+(ggx+-g(x+xAx))*f(x)]/Ax
=lim[(f(x+-f(x)x*g(x+Ax)+(g(x+A
x)-g(x))*f(x)+f(x)*g(x+-f(x)*g(x+Ax)]/Ax
=lim(f(x+-f(xx*g(x+Ax)/Ax+-g(x)^*f(k))t)Ax=f(x)g(x)+f(x)g'(x)
(13)h(x)=f(x)/g(x)
h'(x)
=lim(f(x+Ax)/g(x+(x)g(xx)/Ax
=lim(f(x+Ax)6=lim[(f(x+-f(k)x)f(x))*g(x)-(g(x+A
x)-g(x)+g(x))*f(x)]/(Axg(x)g(x+Ax))
=lim[(f(x+-f(k)x*g(x)-(g(x+A
x)-g(x))*f(x)+f(x)g(x)f(x)g(x)]/(Axg(x)g(x+Ax))
=lim(f(x+-f(x))*g(x)/(Axg(x)g-(g(x+AAk))
x)-g(x))*f(x)/(Axg(x)g(x+Ax))
=f'(x)g(x)/(g(x)*g(x))-f(x)g'(x)/(g(x)*g(x))
=[f'(x)g(x)-f(x)g'(x)]/(g(x)*g(x))x
14)h(x)=f(g(x))
h'(x)
lim[f(g(x+
-f(gx)))]/
2x
lim[f(g(x+
-g(x)+g(x))f(g(x))]/2
另g(x)=u,
g(x+2x-g)(x)=
2)u
lim(f(u+
-2f(uu))/2x
lim(f(u+
-2f(uu))*2u/(
2x*2u)
limf'(u)*
2u/2x
limf(u)*(g(x+-g(x))/x)
2x
=f'(u)*g'(x)=f'(g(x))g'(x)
(反三角函数的导数与三角函数的导数的乘积为1,因为函数与反函数关于
y=x对称,所以导数也关于y=x对称,所以导数的乘积为1)
(15)y=f(x)=arcsinx
则siny=x
(siny)'=cosy
所以
(arcsinx)'=1/(siny)'=1/cosy
=1/VisinyF2
(siny=x)
=1/V-kA2
即f'(x)=1/VA2
(16)y=f(x)=arctanx
则tany=x
(tany)'=1+(tany)八2=1+xT
所以
(arctanx)'=+xT
即f'(x)二+xA2
总结一下
(xAn)'=nxA(n-1)
(sinx)'=cosx
(cosx)'=-sinx
(aAx)'=aAxlna
(eAx)'=eAx
(logaAx)'=1/(xlna)
(lnx)'=1/x
(tanx)'=(secx)A2=1+(tanx)A2(cotx)'=-(cscx)A2=-1-(cotx)A2(secx)'=tanx*secx
(cscx)'=-cotx*cscx
(xAx)'=(lnx+1)*xAx
(arcsinx)'=1/-x91
(arctanx)'=+xA2
[f(x)g(x)]'=f'(x)g(x)+f(x)g'(x)
[f(x)/g(x)]'=[f'(x)g(x)-f(x)g'(x)]/(g(x)*g(x))
[f(g(x))]'=f'(g(x))g'(x)