2x2 - 16x = 20
Divide each term by 2
x2 - 8x = 10
Subtract 10 from both sides
x2 - 8x - 10 = 0
This doesn't factorize nicely, so use the quadratic formula to solve it.
$$x=\frac{-(-8)\pm \sqrt{(-8)^2-4\times1\times (-10)}}{2\times1}$$
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