知A大于B.求证A的三次方大于B的三次方～证明：A>Ba^3-b^3=a^3-a^2b+a^2b-b^3 =a^2(a-b)+b(a^2-b^2) =a^2(a-b)+b(a+b)(a-b) =(a-b)[a^2+b(a+b)] =(a-b)(a^2+ab+b^2)=(a-b)[(a+b/2)^2+(√3b/2)^2]>0(A>B,a-b>0)...