72=x^2-16x

Solution for 72=x^2-16x equation:

72=x^2-16x

We move all terms to the left:

72-(x^2-16x)=0

We get rid of parentheses

-x^2+16x+72=0

We add all the numbers together, and all the variables

-1x^2+16x+72=0

a = -1; b = 16; c = +72;
Δ = b2-4ac
Δ = 162-4·(-1)·72
Δ = 544
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:

$\sqrt{\Delta}=\sqrt{544}=\sqrt{16*34}=\sqrt{16}*\sqrt{34}=4\sqrt{34}$
$x_{1}=\frac{-b-\sqrt{\Delta}}{2a}=\frac{-(16)-4\sqrt{34}}{2*-1}=\frac{-16-4\sqrt{34}}{-2}
$
$x_{2}=\frac{-b+\sqrt{\Delta}}{2a}=\frac{-(16)+4\sqrt{34}}{2*-1}=\frac{-16+4\sqrt{34}}{-2}
$