第1个回答 2011-07-02
(a+b)²=4 (a-b)²=6
a^2 + 2ab + b^2 = 6 (1)
a^2 - 2ab + b^2 = 6/4 (2)
(1)-(2): 4ab = 6 - 6/4 = 9/2 ==> ab = 9/8
(1)+(2): 2(a^2 + b^2) = 6 + 6/4 = 15/2 ==> a^2 + b^2 = 15/4
a²+b²+ab = 15/4 + 9/8 = 39/8
第2个回答 2011-07-02
(a+b)²=4 (a-b)²=6 ,a^2 + 2ab + b^2 = 6,a^2 - 2ab + b^2 = 6/4
a^2+ab+b^2=39/8
第3个回答 2011-07-02
(a+b)²=a²+b²+2ab=4 (1)
(a-b)²=a²+b²-2ab=6 (2)
(1)+(2),得2(a²+b²)=10,故a²+b²=5;
(1)-(2),得4ab=-2,故ab=-1/2.
原式=5-1/2=9/2=4.5.