Verified answer

so far others are wrong...

9)No-domain error when you square a negative you get a positive and if you square root that you dont get what you started with

10)Yes. addition and subtraction are always reversable

11)No-domain error.

give best answer to the one that is correct.

9) yes, you can square them again. You have to be sure that neither side is negative to begin with, however.

10) yes, you can add the number back to both sides.

11) yes, you can multiply both sides by the same number.

all are reversable

9 square both sides

10 add a variable to both sides

11 multiply both sides by variable

9.Yes.

10. Yes, because you can always add back.

11. Yes, you can always multiply back.

Are you dealing with Real numbers and/or matrices?

There are certain groups where these are not necessarily true.