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2x^2-21x-40=0
a = 2; b = -21; c = -40;
Δ = b2-4ac
Δ = -212-4·2·(-40)
Δ = 761
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{-(-21)-\sqrt{761}}{2*2}=\frac{21-\sqrt{761}}{4} $$x_{2}=\frac{-b+\sqrt{\Delta}}{2a}=\frac{-(-21)+\sqrt{761}}{2*2}=\frac{21+\sqrt{761}}{4} $
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