（3xy+10y)+[+5x-(2xy+2y-3x)] =3xy+10y+[+5x-2xy-2y+3x],[原式去括号]=3xy+10y+5x-2xy-2y+3x,[去括号]=3xy-2xy+5x+3x+10y-2y,[合并同类项]=xy+8x+8y=xy+8(x+y),[提取公因式8]=-2+8(3) ,[将xy=-2,x+y=3,代入]=-2+24=...