已知a+b=-2,ab=-5/2,求a(a+b)(a-b)-a(a=b)^2

题目

已知a+b=-2,ab=-5/2,求a(a+b)(a-b)-a(a=b)^2

答案

a(a+b)(a-b)-a(a+b)^2
=a(a+b)[(a-b)-(a+b)]
=a(a+b)*(-2b)
=-2ab(a+b)
=-2*(-5/2)*(-2)
=-10