>>7
xかyのどちらかで整理するのが定石

2x^2-3xy-2y^2+x+3y-1
= 2x^2 -(3y-1)x -(2y^2-3y+1)
= 2x^2 -(3y-1)x -(2y-1)(y-1)
= {2x +(y-1)} {x-(2y-1)}
= (2x+y-1)(x-2y+1)