720=2x^2-36

Solution for 720=2x^2-36 equation:

720=2x^2-36

We move all terms to the left:

720-(2x^2-36)=0

We get rid of parentheses

-2x^2+36+720=0

We add all the numbers together, and all the variables

-2x^2+756=0

a = -2; b = 0; c = +756;
Δ = b2-4ac
Δ = 02-4·(-2)·756
Δ = 6048
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:

$\sqrt{\Delta}=\sqrt{6048}=\sqrt{144*42}=\sqrt{144}*\sqrt{42}=12\sqrt{42}$
$x_{1}=\frac{-b-\sqrt{\Delta}}{2a}=\frac{-(0)-12\sqrt{42}}{2*-2}=\frac{0-12\sqrt{42}}{-4}
=-\frac{12\sqrt{42}}{-4}
=-\frac{3\sqrt{42}}{-1}
$
$x_{2}=\frac{-b+\sqrt{\Delta}}{2a}=\frac{-(0)+12\sqrt{42}}{2*-2}=\frac{0+12\sqrt{42}}{-4}
=\frac{12\sqrt{42}}{-4}
=\frac{3\sqrt{42}}{-1}
$