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求下面两个极限lim x[(x^2+1)^(1/2)-x] x趋近于+∞;lim (tanx-sinx)/x^3 x趋近

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求下面两个极限
lim x[(x^2+1)^(1/2)-x] x趋近于+∞;
lim (tanx-sinx)/x^3 x趋近于0;
求下面两个极限lim x[(x^2+1)^(1/2)-x] x趋近于+∞;lim (tanx-sinx)/x^3 x趋近
lim x[(x^2+1)^(1/2)-x]=lim x/ [(x^2+1)^(1/2)+x]
用洛必达法则=lim 1/[x/(x^2+1)^(1/2)+1]=
lim (x^2+1)^(1/2)/[(x^2+1)^(1/2)+x]=1-limx/ [(x^2+1)^(1/2)+x]
得到2lim x/ [(x^2+1)^(1/2)+x]=1
即 lim x/ [(x^2+1)^(1/2)+x]=1/2
lim x[(x^2+1)^(1/2)-x]=1/2
lim (tanx-sinx)/x^3=lim sinx(1-cosx)/(x^3*cosx)
=lim sinx*2[sin(x/2)]^2/(x^3*cosx)=
lim sinx/x*lim (sin(x/2))^2/(x/2)^2*lim1/2cosx=1/2