x^2+9x-720=0

Solution for x^2+9x-720=0 equation:

x^2+9x-720=0

a = 1; b = 9; c = -720;
Δ = b2-4ac
Δ = 92-4·1·(-720)
Δ = 2961
The delta value is higher than zero, so the equation has two solutions
We use following formulas to calculate our solutions:
$x_{1}=\frac{-b-\sqrt{\Delta}}{2a}$
$x_{2}=\frac{-b+\sqrt{\Delta}}{2a}$

The end solution:

$\sqrt{\Delta}=\sqrt{2961}=\sqrt{9*329}=\sqrt{9}*\sqrt{329}=3\sqrt{329}$
$x_{1}=\frac{-b-\sqrt{\Delta}}{2a}=\frac{-(9)-3\sqrt{329}}{2*1}=\frac{-9-3\sqrt{329}}{2}
$
$x_{2}=\frac{-b+\sqrt{\Delta}}{2a}=\frac{-(9)+3\sqrt{329}}{2*1}=\frac{-9+3\sqrt{329}}{2}
$