lim x趋于无穷大 (1+3/x^3)/(5-3/x^2 +1/x^3)
=1/5那如果x趋于无穷大时，(x^3+3)/(5x^3-3x+1)的3改为x，x趋于无穷大时，(x^3+x)/(5x^3-3x+1)求极限呢lim x趋于无穷大(1+1/x^2)/(5-3/x^2 +1/x^3)
=1/5