18(a+b)^3-12b(b-a)^2=18(a^3+3a^2b+3ab^2+b^3)-12b(b^2-2ab+a^2)=18a^3+54a^2b+54ab^2+18b^3-12b^3+24ab^2-12a^2b=18a^3+42a^2b+78ab^2+6b^3=18a^3+42a^2b+78ab^2+6b^3题目是否有误
