How many nonnegative solutions are there to the equation $x^2 = -4x$?
If I add $4x$ to both sides, I get $x^2 + 4x = 0$. I can factor out an $x$ from the left side and get $x(x+4) = 0$. I get $x = 0$ or $x = -4$. These are the two possible solutions for x, but the problem asks for the nonnegative solutions. That means I only want the solutions that are greater than or equal to zero. Of the two solutions I found, only one of them is nonnegative, namely $x = 0$. Therefore, there is only one nonnegative solution to the equation. 