20+8x(x-11)=-12

Solution for 20+8x(x-11)=-12 equation:

20+8x(x-11)=-12

We move all terms to the left:

20+8x(x-11)-(-12)=0

We add all the numbers together, and all the variables

8x(x-11)+32=0

We multiply parentheses

8x^2-88x+32=0

a = 8; b = -88; c = +32;
Δ = b2-4ac
Δ = -882-4·8·32
Δ = 6720
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:

$\sqrt{\Delta}=\sqrt{6720}=\sqrt{64*105}=\sqrt{64}*\sqrt{105}=8\sqrt{105}$
$x_{1}=\frac{-b-\sqrt{\Delta}}{2a}=\frac{-(-88)-8\sqrt{105}}{2*8}=\frac{88-8\sqrt{105}}{16}
$
$x_{2}=\frac{-b+\sqrt{\Delta}}{2a}=\frac{-(-88)+8\sqrt{105}}{2*8}=\frac{88+8\sqrt{105}}{16}
$