a, 2xy + z + 2x + yz
= (2xy + 2x) + (z + yz)
= 2x.(y + 1) + z.(y + 1)
= (y + 1).(2x + z)
b, x^2 + 2xy + y^2 - xz - yz
= (x^2 + 2xy + y^2) - (xz + yz)
= (x + y)^2 - z.(x + y)
= (x + y).(x + y - z)
c, x^2 - 6x + 9 - 4y^2
= (x^2 - 6x + 9) - 4y^2
= (x - 3)^2 - (2y)^2
= (x - 3 - 2y).(x - 3 + 2y)
d, ay - a + 5y - 5
= (ay - a) + (5y - 5)
= a.(y - 1) + 5.(y - 1)
= (y - 1).(a + 5)
e, xa - ay + 3bx - 3by
= (xa - ay) + (3bx - 3by)
= a.(x - y) + 3b.(x - y)
= (x - y).(a + 3b)