x^2+4=400

Solution for x^2+4=400 equation:

x^2+4=400

We move all terms to the left:

x^2+4-(400)=0

We add all the numbers together, and all the variables

x^2-396=0

a = 1; b = 0; c = -396;
Δ = b2-4ac
Δ = 02-4·1·(-396)
Δ = 1584
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:

$\sqrt{\Delta}=\sqrt{1584}=\sqrt{144*11}=\sqrt{144}*\sqrt{11}=12\sqrt{11}$
$x_{1}=\frac{-b-\sqrt{\Delta}}{2a}=\frac{-(0)-12\sqrt{11}}{2*1}=\frac{0-12\sqrt{11}}{2}
=-\frac{12\sqrt{11}}{2}
=-6\sqrt{11}
$
$x_{2}=\frac{-b+\sqrt{\Delta}}{2a}=\frac{-(0)+12\sqrt{11}}{2*1}=\frac{0+12\sqrt{11}}{2}
=\frac{12\sqrt{11}}{2}
=6\sqrt{11}
$