((x^3+x^2)^1/3=x(1+1/x)^(1/3)=x(1+(1/3)(1/x)+o(1/x)) (x^4-x^3)^1/4=x(1-1/x)^(1/4)=x(1-(1/4)(1/x)+o(1/x)),所以: ((x^3+x^2)^1/3-(x^4-x^3)^1/4) =(1/3+1/4)+xo(1/x)趋于7/12
((x^3+x^2)^1/3=x(1+1/x)^(1/3)=x(1+(1/3)(1/x)+o(1/x)) (x^4-x^3)^1/4=x(1-1/x)^(1/4)=x(1-(1/4)(1/x)+o(1/x)),所以: ((x^3+x^2)^1/3-(x^4-x^3)^1/4) =(1/3+1/4)+xo(1/x)趋于7/12