72=(18-x)x

Solution for 72=(18-x)x equation:

72=(18-x)x

We move all terms to the left:

72-((18-x)x)=0

We add all the numbers together, and all the variables

-((-1x+18)x)+72=0


We calculate terms in parentheses: -((-1x+18)x), so:

(-1x+18)x

We multiply parentheses

-1x^2+18x

Back to the equation:

-(-1x^2+18x)


We get rid of parentheses

1x^2-18x+72=0

We add all the numbers together, and all the variables

x^2-18x+72=0

a = 1; b = -18; c = +72;
Δ = b2-4ac
Δ = -182-4·1·72
Δ = 36
The delta value is higher than zero, so the equation has two solutions
We use following formulas to calculate our solutions:
$x_{1}=\frac{-b-\sqrt{\Delta}}{2a}$
$x_{2}=\frac{-b+\sqrt{\Delta}}{2a}$

$\sqrt{\Delta}=\sqrt{36}=6$
$x_{1}=\frac{-b-\sqrt{\Delta}}{2a}=\frac{-(-18)-6}{2*1}=\frac{12}{2}
=6
$
$x_{2}=\frac{-b+\sqrt{\Delta}}{2a}=\frac{-(-18)+6}{2*1}=\frac{24}{2}
=12
$