若a+b=3,a^2+b^2=4,求ab的值

问题描述:

若a+b=3,a^2+b^2=4,求ab的值

a^2+b^2=4
a^2+b^2+2ab=4+2ab
(a+b)^2= 4+2ab
3^2=4+2ab
ab=2.5