Y=x^2 I know that x= -/+ sqrt(y) but I don`t understand why I do this every time I try to solve "y=x^2" for "x". I know the fact that -2^2=4, and also 2^2=4. and that is why we must have two answers, but I just need to understand how the process really goes, I just want to know the flaw of the logical steps that lead to the conclusion that x=-/+ sqrt(y). I think its about inverse functions, and when I asked my question on Yahoo! answers, I got this answer: The inverse of a function f(x) is defined as I just don`t get how he`s done the last step! huh, it really doesn't make sense to me, since he just applied the inverse -which in this case is sqrt. function- on the last step, which is the thing I`m actually trying to understand how it happened! PS: I`m sorry, I haven`t studied mathematics thoroughly before, nor have I studied logic.. So, actually I don't know if I could put my question in a better way, because I don`t even know where is the problem specifically, I`m just a high school student, trying to understand something out of his book, because he is burning to hell to know how this is happening.