a+b=1,ab=-3,
(a+b)^2=1
a^2+b^2=1+6=7
(a-b)的平方
=a^2+b^2-2ab
=7+6
=13下面还有一题呢。a^3b+2a^2b^2+ab^3
=ab(a^2+2ab+b^2)
=ab(a+b)^2
a+b=2/3,ab=2

所以
ab(a+b)^2
=2x4/9
=8/9