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9x+ay+9y+ax=

7a-7b+an-bn=

ax+ay-x-y=

1-bx-x+b=

xy+2y-2x-4=

9x+ay+9y+ax = (9x+9y) + (ay+ax) = 9 (x+y) + a (y+x) = (x+y) (9+a)

7a-7b+an-bn = (7a-7b) + (an-bn) = 7 (a-b) + n (a-b) = (a-b) (7+n)

ax+ay-x-y = (ax+ay) - (x+y) = a (x+y) - (x+y) = (x+y) (a-1)

1-bx-x+b = (1-x) - (bx-b) = (1-x) - b (x-1) = (1-x) + b (1-x) = (1-x) (1+b)

xy+2y-2x-4 = (2y-4) + (xy-2x) = 2 (y-2) + x (y-2) = (y-2) (2+x)