數學題 化簡 有步驟唔該

1. 63a^2 + 7(b - 5)^2
= 7[9a^2 + (b - 5)^2]

2. (5a - 3)(a - b) + 3b(a - b)
= (a - b)[(5a - 3) + 3b]
= (a - b)(5a + 3b - 3)