Question

如果（a+b)^2=11,(a-b)^2=7,则ab的值为

Answer 1

（a+b)^2=11=a^2+b^2+2ab
,(a-b)^2=7=a^2+b^2-2ab
上式-下式：4=4ab
ab=1

Answer 2

(a+b)^2=11=a^2+2ab+b^2=11 式1
(a-b)^2=7=a^2-2ab+b^2=7 式2
式1-式2=2ab-(-2ab)=11-7
4ab=4
ab=1

Answer 3

ab=1