(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)
(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)
(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

﹙x²－y²－2xy﹚－3﹙﹣x²＋xy﹚－2﹙x²－5/2 xy﹚
＝x²－y²－2xy＋3x²－3xy－2x²＋5xy
＝2x²－y²