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x2-9x=20

We move all terms to the left:

x2-9x-(20)=0

We add all the numbers together, and all the variables

x^2-9x-20=0

a = 1; b = -9; c = -20;

Δ = b^{2}-4ac

Δ = -9^{2}-4·1·(-20)

Δ = 161

The delta value is higher than zero, so the equation has two solutions

We use following formulas to calculate our solutions:$x_{1}=\frac{-b-\sqrt{\Delta}}{2a}$$x_{2}=\frac{-b+\sqrt{\Delta}}{2a}$$x_{1}=\frac{-b-\sqrt{\Delta}}{2a}=\frac{-(-9)-\sqrt{161}}{2*1}=\frac{9-\sqrt{161}}{2} $$x_{2}=\frac{-b+\sqrt{\Delta}}{2a}=\frac{-(-9)+\sqrt{161}}{2*1}=\frac{9+\sqrt{161}}{2} $

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