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x^2+x-640=0
a = 1; b = 1; c = -640;
Δ = b2-4ac
Δ = 12-4·1·(-640)
Δ = 2561
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{-(1)-\sqrt{2561}}{2*1}=\frac{-1-\sqrt{2561}}{2} $$x_{2}=\frac{-b+\sqrt{\Delta}}{2a}=\frac{-(1)+\sqrt{2561}}{2*1}=\frac{-1+\sqrt{2561}}{2} $
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