TITLE: Rewrite equation to solve for $x$, not $y$
QUESTION [5 upvotes]: I am doing calculus integration, and need to show my work for Horizontal slicing (even though Vertical slicing is far easier). 
The equation is $$y= x/\sqrt{2x^2+1}$$
I need to rewrite the equation so that it is $x=\;...$ in order to horizontally slice it (in other words, it should be rewritten so that it is dependent on $y$). 
This isn't exactly a calculus question, although it is being used for calculus. I'm probably missing something that is pretty obvious. 
Any help would be greatly appreciated!

REPLY [6 votes]: Heres a tip:  Take reciprocals.
Notice $$\left( \frac{1}{y}\right)^2=\left( \frac{\sqrt{2x^2+1}}{x}\right)^2=\frac{2x^2+1}{x^2}=2+\frac{1}{x^2}$$
Then we get $$\frac{1}{x^2}=\frac{1}{y^2}-2$$
Take reciprocals again and we find
$$x^2=\frac{1}{\frac{1}{y^2}-2}$$
Take square roots, and we are finished.
Hope that helps
Edit:  Just to make things complete I decided to add the final line: $$x=\pm \sqrt{\frac{y^2}{1-2y^2}}$$