Question

a立方+b立方+3ab的值,不用立方公式怎么求

Answer 1

a^3+b^3+3ab=(a+b)(a^2-ab+b^2)+3ab

=(a+b)((a-b)^2-ab)+3ab

=(a+b)(a-b)^2-ab(a+b)+3ab

=(a+b)(a-b)^2-ab(a+b-3)