720=X*x+1

Solution for 720=X*x+1 equation:

720=X*X+1

We move all terms to the left:

720-(X*X+1)=0

We get rid of parentheses

-X*X-1+720=0

We add all the numbers together, and all the variables

-X*X+719=0

Wy multiply elements

-1X^2+719=0

a = -1; b = 0; c = +719;
Δ = b2-4ac
Δ = 02-4·(-1)·719
Δ = 2876
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:

$\sqrt{\Delta}=\sqrt{2876}=\sqrt{4*719}=\sqrt{4}*\sqrt{719}=2\sqrt{719}$
$X_{1}=\frac{-b-\sqrt{\Delta}}{2a}=\frac{-(0)-2\sqrt{719}}{2*-1}=\frac{0-2\sqrt{719}}{-2}
=-\frac{2\sqrt{719}}{-2}
=-\frac{\sqrt{719}}{-1}
$
$X_{2}=\frac{-b+\sqrt{\Delta}}{2a}=\frac{-(0)+2\sqrt{719}}{2*-1}=\frac{0+2\sqrt{719}}{-2}
=\frac{2\sqrt{719}}{-2}
=\frac{\sqrt{719}}{-1}
$