1-(x²-2xy+y²)= 1-(x-y)²= (1-x+y)*(1+x-y)
4-x²-2xy-y²= 4-(x²+2xy+y²)= 4-(x+y)²= (2-x-y)(2+x+y)
a²-b²-a-b= (a-b)(a+b)-(a+b)= (a+b)(a-b-1)
x³+x²-x-1= x²(x+1)-(x+1)= (x+1)(x²-1)= (x+1)(x-1)(x+1)
x⁴-x³+x-1= x³(x-1)+(x-1)= (x-1)(x³+1)= (x-1)(x+1)(x²-x+1)
