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已知:(a+b)^2=7,(a-b)^2=4,求(a ^2)+(b ^2),ab的值.

(a+b)^2=(a ^2)+2ab+(b ^2)=7
(a-b)^2=(a ^2)-2ab+(b ^2)=4
2[(a ^2)+(b ^2)]=11
(a ^2)+(b ^2)=5.5
(a ^2)+2ab+(b ^2)=5.5+2ab=7
2ab=1.5,ab=3/4