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x2-40x+399=0
We add all the numbers together, and all the variables
x^2-40x+399=0
a = 1; b = -40; c = +399;
Δ = b2-4ac
Δ = -402-4·1·399
Δ = 4
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}$$x_{2}=\frac{-b+\sqrt{\Delta}}{2a}$$\sqrt{\Delta}=\sqrt{4}=2$$x_{1}=\frac{-b-\sqrt{\Delta}}{2a}=\frac{-(-40)-2}{2*1}=\frac{38}{2} =19 $$x_{2}=\frac{-b+\sqrt{\Delta}}{2a}=\frac{-(-40)+2}{2*1}=\frac{42}{2} =21 $
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