When do you use plus/minus signs with roots?

[AznBoi]

Ok I'm a little confused with this:

16x-y^4=0

When you solve for (y) you get: y= plus/minus 4th root(16x) right?
There for it isn't a function.

What about y=sq.rt.(1-x)? Does it have the plus/minus automatically? Do you only put the plus/minus sign if you solve for y?

I just don't get when you have to put the plus/minus in front of the sq.rt. Do you always have to put one there? or only if you solve for y, etc.?

 

[arildno]

Well, the even root of a number is DEFINED to be the positive number.
That is, by definition, $\sqrt{1-x}$ is a positive number.

When you solve for y, however, you must remember that not only do you have the positive, even root as a solution, but also the negative of that number.

 

[AznBoi]

Oh ok. So if they give you an equation that has no plus/minus infront of it, then the equation is POSITIVE. However, if you solve for y and get a sq.rt. then you must put the plus/minus sign right? Thanks.