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-x^2+21x+107=0
We add all the numbers together, and all the variables
-1x^2+21x+107=0
a = -1; b = 21; c = +107;
Δ = b2-4ac
Δ = 212-4·(-1)·107
Δ = 869
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{869}}{2*-1}=\frac{-21-\sqrt{869}}{-2} $$x_{2}=\frac{-b+\sqrt{\Delta}}{2a}=\frac{-(21)+\sqrt{869}}{2*-1}=\frac{-21+\sqrt{869}}{-2} $
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