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.7x^2+21x-28=0
a = .7; b = 21; c = -28;
Δ = b2-4ac
Δ = 212-4·.7·(-28)
Δ = 519.4
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{519.4}}{2*.7}=\frac{-21-\sqrt{519.4}}{1.4} $$x_{2}=\frac{-b+\sqrt{\Delta}}{2a}=\frac{-(21)+\sqrt{519.4}}{2*.7}=\frac{-21+\sqrt{519.4}}{1.4} $
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