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-3x^2+21x+90=0
a = -3; b = 21; c = +90;
Δ = b2-4ac
Δ = 212-4·(-3)·90
Δ = 1521
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{1521}=39$$x_{1}=\frac{-b-\sqrt{\Delta}}{2a}=\frac{-(21)-39}{2*-3}=\frac{-60}{-6} =+10 $$x_{2}=\frac{-b+\sqrt{\Delta}}{2a}=\frac{-(21)+39}{2*-3}=\frac{18}{-6} =-3 $
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