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-4x^2+28x-40=0
a = -4; b = 28; c = -40;
Δ = b2-4ac
Δ = 282-4·(-4)·(-40)
Δ = 144
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{144}=12$$x_{1}=\frac{-b-\sqrt{\Delta}}{2a}=\frac{-(28)-12}{2*-4}=\frac{-40}{-8} =+5 $$x_{2}=\frac{-b+\sqrt{\Delta}}{2a}=\frac{-(28)+12}{2*-4}=\frac{-16}{-8} =+2 $
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