1, = ( x^2 -y^2) -(x+y) = (x-y) .(x+y) -(x+y) = (x+y).(x-y-1)
2, = (x^2-y^2) +(x-y) = (x-y).(x+y) +(x-y) = (x-y) .(x+y+1)
3, = (3x-3y) +(x^2-y^2) = 3.(x-y) + (x-y).(x+y) = (x-y).(3+x+y)
4, = (5x-5y) +(x^2-y^2) = 5.(x-y) + (x-y).(x+y)= (x-y).(5+x+y)
5, = (x^2-y^2)-(5x+5y) = (x-y).(x+y)-5.(x+y) =(x+y).(x-y-5)
6,= (x^2-y^2)+(2x-2y) =(x+y).(x-y)+2.(x-y)=(x-y).(x+y+2)
7, = (x^2-4y^2)+(x+2y)= (x-2y).(x+2y)+(x+2y)= (x+2y).(x-2y+1)
8, = (x^2-y^2)-2.(x+y)= (x+y).(x-y)-2.(x+y)=(x+y).(x-y-2)
9,= (x^2-4y^2)+(2x+4y) =(x-2y).(x+2y)+2.(x+2y)=(x+2y).(x-2y+2)
10,=x.(x-y) +(x-y).(x+y)= (x-y).( 2x+y) 11, = (x-y).(x+y)+10.(x-y)=(x-y).(x+y+10 )
12, (x-y).(x+y)+20.(x+y)=(x+y).(x-y+20) 13, = (2x-3y).(2x+3y)-2.(2x+3y)=(2x+3y).(2x-3y-2)
14, = (x-y).(x^2+xy+y^2)+7.(x-y).(x+y) = (x-y).( x^2+xy+y^2 +7x+7y)
15, = (x-y).(x^2+xy+y^2) +4.(x-y) =(x-y).( x^2 +xy+y^2 +4)
16, = (x+y).(x^2-xy+y^2) +2.(x+y) = (x+y) .( x^2-xy+y^2+2)
17, = (x-y).(x^2+xy+y^2) -2xy.(x-y) =(x-y).( x^2 +y^2 -xy)
18, = x.( x^2 -4x +4 -y^2)