x(5x+3)=4000

Solution for x(5x+3)=4000 equation:

x(5x+3)=4000

We move all terms to the left:

x(5x+3)-(4000)=0

We multiply parentheses

5x^2+3x-4000=0

a = 5; b = 3; c = -4000;
Δ = b2-4ac
Δ = 32-4·5·(-4000)
Δ = 80009
The delta value is higher than zero, so the equation has two solutions
We use following formulas to calculate our solutions:
$x_{1}=\frac{-b-\sqrt{\Delta}}{2a}$
$x_{2}=\frac{-b+\sqrt{\Delta}}{2a}$

$x_{1}=\frac{-b-\sqrt{\Delta}}{2a}=\frac{-(3)-\sqrt{80009}}{2*5}=\frac{-3-\sqrt{80009}}{10}
$
$x_{2}=\frac{-b+\sqrt{\Delta}}{2a}=\frac{-(3)+\sqrt{80009}}{2*5}=\frac{-3+\sqrt{80009}}{10}
$