Let $f(x) = \sqrt{ax^2 + bx}$. For how many real values of $a$ is there at least one positive value of $b$ for which the domain of $f$ and the range of $f$ are the same set?
<|im_start|>system
You are a helpful assistant.<|im_end|>
<|im_start|>user
Let $f(x) = \sqrt{ax^2 + bx}$. For how many real values of $a$ is there at least one positive value of $b$ for which the domain of $f$ and the range of $f$ are the same set?
Please reason step by step, and put your final answer within \boxed{{}}.<|im_end|>
<|im_start|>assistant

user
2
Let $f(x) = \sqrt{ax^2 + bx}$. For how many real values of $a$ is there at least one positive value of $b$ for which the domain of $f$ and the range of $f$ are the same set?
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