$$-x^2+\frac{20}{10}x-\frac{28}{10} = 0$$
Answer
$$ \begin{matrix}x_1 = 1+\dfrac{ 3 \sqrt{ 5}}{ 5 }i & x_2 = 1-\dfrac{ 3 \sqrt{ 5}}{ 5 }i \\[1 em] \end{matrix} $$
Explanation
$$ \begin{aligned} -x^2+\frac{20}{10}x-\frac{28}{10} &= 0&& \text{multiply ALL terms by } \color{blue}{ 10 }. \\[1 em]-10x^2+10 \cdot \frac{20}{10}x-10\cdot\frac{28}{10} &= 10\cdot0&& \text{cancel out the denominators} \\[1 em]-10x^2+20x-28 &= 0&& \\[1 em] \end{aligned} $$
$ -10x^{2}+20x-28 = 0 $ is a quadratic equation.
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