I've done math problems on some paper, and there are no solutions given.

1. Simplify

(My) solution:

Two solutions?

Now, what if you've "gained" some (and which?) solution by squaring the original?

2. Simplify

a)

b) (For what does the following expression exist?)(If the solution is correct) what is now the answer (on "expression exists for whata?"), everya?

3. Solve

Again, what if you've "gained" some solution by squaring the original? What are considered best practises in solving such?