Question

Is a+b+a+b and 2(a+ b) equivalent?

Answer 1

This is true, because of the distributive property.  You can expand 2(a + b) to be a + b + a + b

Answer 2

Yes bc if you combine like terms u have 2 "a"s and one b so that would be the same as saying 2a and b so your answer is:
Yes.