(x²-y²-2xy)-3(-x²+xy)-2(x²-二分之五xy)

问题描述:

(x²-y²-2xy)-3(-x²+xy)-2(x²-二分之五xy)

(x²-y²-2xy)-3(-x²+xy)-2(x²-二分之五xy)
=x^2-y^2-2xy+3x^2-3xy-2x^2+5xy
=2x^2-y^2