2xy - 3xy^2 = xy (2 - 3y)
8b^4 + 2b^3 = 2b^3 • (4b + 1)
x (x - y) + a (x - y) = (x + a) • (x - y)
2a - 2b + ca - cb = (2 + c) • (a - b)
2a - ac - 2c + c^2 = (a - c) • (2 - c)
bx + by - x - y - ax - ay = b (x + y) - (x + y) - a (x + y) = (x + y) (b - 1 - a)