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21x^2+69x+20=0
a = 21; b = 69; c = +20;
Δ = b2-4ac
Δ = 692-4·21·20
Δ = 3081
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{-(69)-\sqrt{3081}}{2*21}=\frac{-69-\sqrt{3081}}{42} $$x_{2}=\frac{-b+\sqrt{\Delta}}{2a}=\frac{-(69)+\sqrt{3081}}{2*21}=\frac{-69+\sqrt{3081}}{42} $
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