If a quadratic equation has solutions, the standard procedure will always work: given an equation like
The solutions (if any) are given by
In your case, you have
So the formula becomes
Anyway, this is quite a special case, because you're missing the linear term (since )
This means that you can solve equations like these more easily: rearrange the equation to make it look like . In your case, it becomes
Divide both sides by 9:
Now, you know that the square of a number equals 1/9. By definition, it means that this number is the square root of 1/9. Nevertheless, both the square root and its opposite are solutions of the equation, because the minus sign will cancel out when squaring.
So, in general, you have
which of course makes sense, if you're using real numbers, only if c/a>0.
In your case, this becomes