a+b=6,ab=4,求
a²+b²
=( a+b)² -2ab
= 6x6 - 2 x 4
= 36 - 8
= 28
（a-b）²
= ( a+b)² -4ab
= 6x6 - 4x 4
= 36 - 16
= 20
已知a+b=6,ab=4,求a²+b²与（a-b）²的值
a+b=6,ab=4,求
a²+b²
=( a+b)² -2ab
= 6x6 - 2 x 4
= 36 - 8
= 28
（a-b）²
= ( a+b)² -4ab
= 6x6 - 4x 4
= 36 - 16
= 20