720=x*x-1*x-2

Solution for 720=x*x-1*x-2 equation:

720=x*x-1x-2

We move all terms to the left:

720-(x*x-1x-2)=0

We add all the numbers together, and all the variables

-(-1x+x*x-2)+720=0

We get rid of parentheses

1x-x*x+2+720=0

We add all the numbers together, and all the variables

x-x*x+722=0

Wy multiply elements

-1x^2+x+722=0

a = -1; b = 1; c = +722;
Δ = b2-4ac
Δ = 12-4·(-1)·722
Δ = 2889
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:

$\sqrt{\Delta}=\sqrt{2889}=\sqrt{9*321}=\sqrt{9}*\sqrt{321}=3\sqrt{321}$
$x_{1}=\frac{-b-\sqrt{\Delta}}{2a}=\frac{-(1)-3\sqrt{321}}{2*-1}=\frac{-1-3\sqrt{321}}{-2}
$
$x_{2}=\frac{-b+\sqrt{\Delta}}{2a}=\frac{-(1)+3\sqrt{321}}{2*-1}=\frac{-1+3\sqrt{321}}{-2}
$