x(x-1)-(x²+y)=3 求2分之x²+y²+xy的值

问题描述:

x(x-1)-(x²+y)=3 求2分之x²+y²+xy的值

∵x(x-1)-(x²+y)=3
∴x²-x-x²-y=3
∴x+y=-3
∴(x²+y²)/2+xy
=(x²+y²+2xy)/2
=(x+y)²/2
=9/2