It's a simple problem that for some reason I can't remember how to do... Just set me in the right direction

square root of (x^2 + 1) = 0

I'm trying to find all possible numbers that will get that to equal zero. The square root is throwing me off. Do I square both sides, getting

x^2 + 1 = 0

x^2 = -1

x = +or- square root of -1

but you can't take the square root of a negative number?