2.2x²-5xy+2y²+3x-3y+1
=(x-2y)(2x-y)+(x-2y)+2x-y+1
=(x-2y)(2x-y+1)+(2x-y+1)
=(x-2y+1)(2x-y+1)
3.2x²-7xy+6y²+2x-y-12
=(x-2y)(2x-3y)-4x+8y+6x-9y-12
=(x-2y)(2x-3y)-4(x-2y)+3(2x-3y)-12
=(x-2y+3)(2x-3y-4)
4.a²-b²+4a+2b+3
=a²+4a+4-b²+2b-1
=(a²+4a+4)-(b²-2b+1)
=(a+2)²-(b-1)²
=(a+2+b-1)(a+2-b+1)