square both sides
With equations the involve squaring, it is important to check your solutions. This is because the process of squaring an equations is not reversible.
From going to your first step to your second step you introduce an additional equation into the problem.
The expression could have either come form squaring this or , so the solutions to obtain through this process could be solutions to either equation. additional solutions obtained form squaring an equation are called extraneous roots. In this case you don't have the problem but watch out for them.