题目: 已知x+y=6,xy=8,则x2+y2=______,(x-y)2=______. 答案: ∵x+y=6,∴x2+2xy+y2=36,∵xy=8,∴x2+y2=36-2×8=20;∴(x-y)2=x2-2xy+y2=20-2×8=4.故答案为:x2+y2=20,(x-y)2=4.