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-x2-9x+7=0
We add all the numbers together, and all the variables
-1x^2-9x+7=0
a = -1; b = -9; c = +7;
Δ = b2-4ac
Δ = -92-4·(-1)·7
Δ = 109
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{-(-9)-\sqrt{109}}{2*-1}=\frac{9-\sqrt{109}}{-2} $$x_{2}=\frac{-b+\sqrt{\Delta}}{2a}=\frac{-(-9)+\sqrt{109}}{2*-1}=\frac{9+\sqrt{109}}{-2} $
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