已知a+b=3,ab=-2,求a^2+b^2及（a-b）^2的值

题目

已知a+b=3,ab=-2,求a^2+b^2及（a-b）^2的值

答案

a²+b²
=(a+b)²-2ab
=3²-2×(-2)
=9+4
=13
(a-b)²
=(a+b)²-4ab
=3²-4×(-2)
=9+8
=17