Data Sufficiency

I have always thought that when GMAT gives you a Square Root....it only has one possible answer, and hat is its positive solution (the negative solution is not taken on account).

So I am having problems understanding thid problem:

What is the value of x?

1) Squareroot(x^4)=9

2) The average of x, 6x, and 3 is -2

Statement 2 is SUFF.

But what about statement 1? One would think that "Squareroot(x^4)=9" is the same has saying "x^2=9" so x has two possible answers: +3 and -3. BUT I thought that when GMAT writes "Squareroot" it is only refering to the positive value of the root...that is +3.....So I chose D, but the correct answer is B because it says that satement 1 gives two possible answer (+3 and -3).

Can someone please explain me if its true or not that when GMAT gives us a Squareroot it only has one possible answer (the positive value)??

Thanks! I am bit confused...

chris,
sq rt(x ^ 4) =9 in which case x ^ 2 = 3. hence value of x could be
+ or -ve (sq rt 3) thats why a is not sufficient.

Yes I know that, the thing is that when GMAT writes "squareroot" its only refering to the positive value...that is my question... :

Look at it this way...

Lets say, x^4 = y

sqrt(y) = 9

So, y = 81 = x^4

So x can be +3 or -3