400=x(2x+9)

Solution for 400=x(2x+9) equation:

400=x(2x+9)

We move all terms to the left:

400-(x(2x+9))=0


We calculate terms in parentheses: -(x(2x+9)), so:

x(2x+9)

We multiply parentheses

2x^2+9x

Back to the equation:

-(2x^2+9x)


We get rid of parentheses

-2x^2-9x+400=0

a = -2; b = -9; c = +400;
Δ = b2-4ac
Δ = -92-4·(-2)·400
Δ = 3281
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{-(-9)-\sqrt{3281}}{2*-2}=\frac{9-\sqrt{3281}}{-4}
$
$x_{2}=\frac{-b+\sqrt{\Delta}}{2a}=\frac{-(-9)+\sqrt{3281}}{2*-2}=\frac{9+\sqrt{3281}}{-4}
$