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x^2+21x+12=0
a = 1; b = 21; c = +12;
Δ = b2-4ac
Δ = 212-4·1·12
Δ = 393
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{393}}{2*1}=\frac{-21-\sqrt{393}}{2} $$x_{2}=\frac{-b+\sqrt{\Delta}}{2a}=\frac{-(21)+\sqrt{393}}{2*1}=\frac{-21+\sqrt{393}}{2} $
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