先化简再求职:3xy+3x^2+2y-3xy-2x^2其中x=-2 y=1已知x^2+xy=2,y^2+xy=5,求1/2x^2+xy+1/2y^

问题描述:

先化简再求职:3xy+3x^2+2y-3xy-2x^2其中x=-2 y=1
已知x^2+xy=2,y^2+xy=5,求1/2x^2+xy+1/2y^

根据已知,得出(x+y)²=7
1/2x²+xy+1/2y²
=(x²+2xy+y²)/2
=(x+y)²/2
=7/2