a^2 - ab - bc - c^2 = (a + c)(a - b) - c(a + c) = (a + c)(a - c - b)
3x - 2x^2 + 3y - 2xy = -x(2x - 3) + y(3 - 2x) = (3 - 2x)(y - x)
20z^2k + 2z - 5k + 1 = 2(10z^2 + 1) - 1(5k - 1) = (2z + 1)(10z + 1)
a^2 - ab - bc - c^2 = (a + c)(a - b) - c(a + c) = (a + c)(a - c - b)
3x - 2x^2 + 3y - 2xy = -x(2x - 3) + y(3 - 2x) = (3 - 2x)(y - x)
20z^2k + 2z - 5k + 1 = 2(10z^2 + 1) - 1(5k - 1) = (2z + 1)(10z + 1)