I seem to be stuck on some seemingly simple algebra;
The aim is to rearrange $$y = 3 + \sqrt{x + 2}$$ for $x$. 

My working is as follows, I just square everything: $$y^2 = 3^2 + x + 2$$
It is clear to me that this is incorrect, however I don't understand why one has to take the 3 over to the other side before squaring everything.
Correct answer: $$(y-3)^2 = x+2$$