learning it in the first time but usually they give a little bit of construct there, they usually say for a and b greater than or equal to zero so thats where they listes property this is true for a and b be greater or equal to zero and in particular it's false if both a and b are negative, Now I've said that, I've just spend lat three minutes saying that people who tell you this is wrong are wrong but with that I said I do say you have to be a little bit careful about it, when we take traditional principal square roots so you take thi principal square root of 4, we know this is positive 2 that 4 actually has two square roots, negative 2 ia also a square root of 4, if you have negative 2 times negaive 2 is also equal to 4, this radical symbol here means principal square root or when we just dealing with real numbers non imaginary non complex numbers you can really ??? as positive square root, this is two square roots, positive and negative 2 if you have this radical symbol right here, principal square roots it means the positive square root of 2.