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-7x^2+2x+9=0
a = -7; b = 2; c = +9;
Δ = b2-4ac
Δ = 22-4·(-7)·9
Δ = 256
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}$$x_{2}=\frac{-b+\sqrt{\Delta}}{2a}$$\sqrt{\Delta}=\sqrt{256}=16$$x_{1}=\frac{-b-\sqrt{\Delta}}{2a}=\frac{-(2)-16}{2*-7}=\frac{-18}{-14} =1+2/7 $$x_{2}=\frac{-b+\sqrt{\Delta}}{2a}=\frac{-(2)+16}{2*-7}=\frac{14}{-14} =-1 $
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