X(2x+4)=400

Solution for X(2x+4)=400 equation:

X(2X+4)=400

We move all terms to the left:

X(2X+4)-(400)=0

We multiply parentheses

2X^2+4X-400=0

a = 2; b = 4; c = -400;
Δ = b2-4ac
Δ = 42-4·2·(-400)
Δ = 3216
The delta value is higher than zero, so the equation has two solutions
We use following formulas to calculate our solutions:
$X_{1}=\frac{-b-\sqrt{\Delta}}{2a}$
$X_{2}=\frac{-b+\sqrt{\Delta}}{2a}$

The end solution:

$\sqrt{\Delta}=\sqrt{3216}=\sqrt{16*201}=\sqrt{16}*\sqrt{201}=4\sqrt{201}$
$X_{1}=\frac{-b-\sqrt{\Delta}}{2a}=\frac{-(4)-4\sqrt{201}}{2*2}=\frac{-4-4\sqrt{201}}{4}
$
$X_{2}=\frac{-b+\sqrt{\Delta}}{2a}=\frac{-(4)+4\sqrt{201}}{2*2}=\frac{-4+4\sqrt{201}}{4}
$