1.
(x+y)-4(x+y)+3
=-3(x+y)+3
=-3(x+y-1)
2.
4a²-b²+6a-3b
=(2a+b)(2a-b)+3(2a-b)
=(2a-b)(2a+b+3)
3.
x²-2xy+y²-5x+5y-6
=(x-y)²-5(x-y)-6
=(x-y-6)(x-y+1)