(2x-4)(9x+1)=0

Solution for (2x-4)(9x+1)=0 equation:

(2x-4)(9x+1)=0

We multiply parentheses ..

(+18x^2+2x-36x-4)=0

We get rid of parentheses

18x^2+2x-36x-4=0

We add all the numbers together, and all the variables

18x^2-34x-4=0

a = 18; b = -34; c = -4;
Δ = b2-4ac
Δ = -342-4·18·(-4)
Δ = 1444
The delta value is higher than zero, so the equation has two solutions
We use following formulas to calculate our solutions:
$x_{1}=\frac{-b-\sqrt{\Delta}}{2a}$
$x_{2}=\frac{-b+\sqrt{\Delta}}{2a}$

$\sqrt{\Delta}=\sqrt{1444}=38$
$x_{1}=\frac{-b-\sqrt{\Delta}}{2a}=\frac{-(-34)-38}{2*18}=\frac{-4}{36}
=-1/9
$
$x_{2}=\frac{-b+\sqrt{\Delta}}{2a}=\frac{-(-34)+38}{2*18}=\frac{72}{36}
=2
$