2x^2+5x=400

Solution for 2x^2+5x=400 equation:

2x^2+5x=400

We move all terms to the left:

2x^2+5x-(400)=0

a = 2; b = 5; c = -400;
Δ = b2-4ac
Δ = 52-4·2·(-400)
Δ = 3225
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:

$\sqrt{\Delta}=\sqrt{3225}=\sqrt{25*129}=\sqrt{25}*\sqrt{129}=5\sqrt{129}$
$x_{1}=\frac{-b-\sqrt{\Delta}}{2a}=\frac{-(5)-5\sqrt{129}}{2*2}=\frac{-5-5\sqrt{129}}{4}
$
$x_{2}=\frac{-b+\sqrt{\Delta}}{2a}=\frac{-(5)+5\sqrt{129}}{2*2}=\frac{-5+5\sqrt{129}}{4}
$