100x+x^2=3900

Solution for 100x+x^2=3900 equation:

100x+x^2=3900

We move all terms to the left:

100x+x^2-(3900)=0

a = 1; b = 100; c = -3900;
Δ = b2-4ac
Δ = 1002-4·1·(-3900)
Δ = 25600
The delta value is higher than zero, so the equation has two solutions
We use following formulas to calculate our solutions:
$x_{1}=\frac{-b-\sqrt{\Delta}}{2a}$
$x_{2}=\frac{-b+\sqrt{\Delta}}{2a}$

$\sqrt{\Delta}=\sqrt{25600}=160$
$x_{1}=\frac{-b-\sqrt{\Delta}}{2a}=\frac{-(100)-160}{2*1}=\frac{-260}{2}
=-130
$
$x_{2}=\frac{-b+\sqrt{\Delta}}{2a}=\frac{-(100)+160}{2*1}=\frac{60}{2}
=30
$