Factorize each of the following expressions:
[3 (a – b)]2 – [10 (x – y)]2
= [3 (a – b) + 10 (x + y)] [3 (a – b) – 10 (x – y)]
= [3a – 3b + 10x – 10y] [3a – 3b – 10x + 10y]