I'm not quite sure of what the equation is. It just doesn't make sense to me. What you have written is either

or

Neither of which should pose a problem.

I'm going to assume that you wrote it wrong and meant:

<-- Square both sides

which you can solve using the quadratic formula:

The bad news is that whenever you square both sides of an equation you should always check to make sure you haven't added a new solution and these forms are messy to substitute back into the original equations. I'll give you peace of mind by telling you that only the "+" solution is correct.

-Dan