x³z + x²yz - x²z² - xyz²
= xz(x² + xy - xz - yz)
= xz[(x² + xy) - (xz + yz)]
= xz[x(x + y) - z(x + y)]
= xz(x + y)(x - z)
-----------
a²x + a²y + ax + ay + x + y
= (a²x + a²y) + (ax + ay) + (x + y)
= a²(x + y) + a(x + y) + (x + y)
= (x + y)(a² + a + 1)
-----------
a² + 2ab + b² - c² + 2cd - d²
= (a² + 2ab + b²) - (c² - 2cd + d²)
= (a + b)² - (c - d)²
= [(a + b) - (c - d)][(a + b) + (c - d)]
= (a + b - c + d)(a + b + c - d)
------------
z² - (x - 1)² + 2(x - 1) - 1
= z² - [(x - 1)² - 2(x - 1) + 1]
= z² - (x - 1 - 1)²
= z² - (x - 2)²
= (z - x + 2)(z + x - 2)



