DS 19.11 Divisibility

[bmwhype]

If A & B are positive integers, is a^2 + b^2 divisible by 5?

1. 2AB is divisible by 5
2. A-B is divisible by 5


Can someone walk me thru the solution

[chandak_anand]

C

a^2 + b^2 = (a-b)^2 + 2ab
since both (a-b) and 2ab divisible by 5,a^2 + b^2 is divisible by 5.