Question

1/18x^2-1/9x=18

Answer 1

Just to be clear, which did you mean of:
\[\frac{1}{18}x^2-\frac{1}{9}x=18\\
\frac{1}{18x^2}-\frac{1}{9x}=18
\]

Answer 2

Well, it it is the first one, I would multiply the whole thing through by 18 to get rid of the fraction. That makes it a little easier to put into \(Ax+By+C=0\) form and solve. If it is the second, common denominator, do the subtraction, get the denominator out through multiplication, subtract things from one side to the other, and then you will have it in a solvable form.