* ax+bx+ay+by=x.(a+b)+y.(a+b)=(x+y).(a+b)
* x3-x2+x-1=x2.(x-1)+(x-1)=(x-1).(x2+1)
* xy-4x-4y+16= x(y-4)-4(y-4) = (y-4).(x-4)
*a²-ba-a+ba-1=a(a-b)-(a-b)a-1=a-b
*4ab-2a-2b²+b2a-b=2a(2b-1)-b(2b-1)a-1=(2b-1).(2a-b)2a-b=2b-1
*3ab-3xb+xy-ayx-a=3b(a-x)-y(a-x)x-a=(a-x).(3b-y)x-a=(x-a).(y-3b)x-a=y-3b
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