$$ \begin{aligned} x(x-2) &= x^2-9&& \text{simplify left side} \\[1 em]x^2-2x &= x^2-9&& \text{move all terms to the left hand side } \\[1 em]x^2-2x-x^2+9 &= 0&& \text{simplify left side} \\[1 em]x^2-2x-x^2+9 &= 0&& \\[1 em]-2x+9 &= 0&& \text{ move the constants to the right } \\[1 em]-2x &= -9&& \text{ divide both sides by $ -2 $ } \\[1 em]x &= \frac{-9}{-2}&& \\[1 em]x &= \frac{9}{2}&& \\[1 em] \end{aligned} $$

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