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x^2-21x-16=0
a = 1; b = -21; c = -16;
Δ = b2-4ac
Δ = -212-4·1·(-16)
Δ = 505
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{505}}{2*1}=\frac{21-\sqrt{505}}{2} $$x_{2}=\frac{-b+\sqrt{\Delta}}{2a}=\frac{-(-21)+\sqrt{505}}{2*1}=\frac{21+\sqrt{505}}{2} $
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