恆等式與因式分解

1.
若題目是
ax - ay + by - bx
= a(x - y) - b(x - y)
= (a - b)(x - y)

若題目是
ax - ay - by + bx
= a(x - y) + b(x - y)
= (a + b)(x - y)

2.
2hk - 2kt + 3h - 3t
= 2k(h - t) + 3(h - t)
= (2k + 3)(h - t)

3.
3mn - mp + 6nq - 2pq
= m(3n - p) + 2q(3n - p)
= (m + 2q)(3n - p)