x^2-4x=213

Solution for x^2-4x=213 equation:

x^2-4x=213

We move all terms to the left:

x^2-4x-(213)=0

a = 1; b = -4; c = -213;
Δ = b2-4ac
Δ = -42-4·1·(-213)
Δ = 868
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:

$\sqrt{\Delta}=\sqrt{868}=\sqrt{4*217}=\sqrt{4}*\sqrt{217}=2\sqrt{217}$
$x_{1}=\frac{-b-\sqrt{\Delta}}{2a}=\frac{-(-4)-2\sqrt{217}}{2*1}=\frac{4-2\sqrt{217}}{2}
$
$x_{2}=\frac{-b+\sqrt{\Delta}}{2a}=\frac{-(-4)+2\sqrt{217}}{2*1}=\frac{4+2\sqrt{217}}{2}
$