216=4x^2+8x+16

Solution for 216=4x^2+8x+16 equation:

216=4x^2+8x+16

We move all terms to the left:

216-(4x^2+8x+16)=0

We get rid of parentheses

-4x^2-8x-16+216=0

We add all the numbers together, and all the variables

-4x^2-8x+200=0

a = -4; b = -8; c = +200;
Δ = b2-4ac
Δ = -82-4·(-4)·200
Δ = 3264
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:

$\sqrt{\Delta}=\sqrt{3264}=\sqrt{64*51}=\sqrt{64}*\sqrt{51}=8\sqrt{51}$
$x_{1}=\frac{-b-\sqrt{\Delta}}{2a}=\frac{-(-8)-8\sqrt{51}}{2*-4}=\frac{8-8\sqrt{51}}{-8}
$
$x_{2}=\frac{-b+\sqrt{\Delta}}{2a}=\frac{-(-8)+8\sqrt{51}}{2*-4}=\frac{8+8\sqrt{51}}{-8}
$