lim(x→∞)(3x^3-4x^2+2)/(7x^3+5x^2-3)=

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lim(x→∞)(3x^3-4x^2+2)/(7x^3+5x^2-3)=
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lim(x→∞)(3x^3-4x^2+2)/(7x^3+5x^2-3)=
lim(x→∞)(3x^3-4x^2+2)/(7x^3+5x^2-3)=

lim(x→∞)(3x^3-4x^2+2)/(7x^3+5x^2-3)=
lim(x→∞)(3x³-4x²+2)/(7x³+5x²-3)=lim(x→∞)[3-(4/x)+(2/x³)]/[7+(5/x)-(3/x³)]=3/7

这种问题,x→∞的极限,只用看最高次项的系数比,
因此lim(x→∞)(3x^3-4x^2+2)/(7x^3+5x^2-3)=3/7

只看指数最大的项的系数即可,其他项均为小量
lim(x→∞)(3x^3-4x^2+2)/(7x^3+5x^2-3)=(3x^3)/(7x^3)=3/7

=3/7