X(18-2x)=40

Solution for X(18-2x)=40 equation:

X(18-2X)=40

We move all terms to the left:

X(18-2X)-(40)=0

We add all the numbers together, and all the variables

X(-2X+18)-40=0

We multiply parentheses

-2X^2+18X-40=0

a = -2; b = 18; c = -40;
Δ = b2-4ac
Δ = 182-4·(-2)·(-40)
Δ = 4
The delta value is higher than zero, so the equation has two solutions
We use following formulas to calculate our solutions:
$X_{1}=\frac{-b-\sqrt{\Delta}}{2a}$
$X_{2}=\frac{-b+\sqrt{\Delta}}{2a}$

$\sqrt{\Delta}=\sqrt{4}=2$
$X_{1}=\frac{-b-\sqrt{\Delta}}{2a}=\frac{-(18)-2}{2*-2}=\frac{-20}{-4}
=+5
$
$X_{2}=\frac{-b+\sqrt{\Delta}}{2a}=\frac{-(18)+2}{2*-2}=\frac{-16}{-4}
=+4
$