-9^3+30x^2+71x+20=0

Solution for -9^3+30x^2+71x+20=0 equation:

-9^3+30x^2+71x+20=0

We add all the numbers together, and all the variables

30x^2+71x-709=0

a = 30; b = 71; c = -709;
Δ = b2-4ac
Δ = 712-4·30·(-709)
Δ = 90121
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{-(71)-\sqrt{90121}}{2*30}=\frac{-71-\sqrt{90121}}{60}
$
$x_{2}=\frac{-b+\sqrt{\Delta}}{2a}=\frac{-(71)+\sqrt{90121}}{2*30}=\frac{-71+\sqrt{90121}}{60}
$