[itex]\frac{1}{x^4}=(\frac{1}{x})^4[/itex] [itex]\sqrt{(\frac{1}{x})^4}=\pm(\frac{1}{x})^2 [/itex] [itex]\sqrt{(\frac{1}{x})^2}=\pm\frac{1}{x} [/itex]
Are we assuming x is real here? Because there's two other possibilities for x that yield the same answer.