121=x^2+8x

Solution for 121=x^2+8x equation:

121=x^2+8x

We move all terms to the left:

121-(x^2+8x)=0

We get rid of parentheses

-x^2-8x+121=0

We add all the numbers together, and all the variables

-1x^2-8x+121=0

a = -1; b = -8; c = +121;
Δ = b2-4ac
Δ = -82-4·(-1)·121
Δ = 548
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:

$\sqrt{\Delta}=\sqrt{548}=\sqrt{4*137}=\sqrt{4}*\sqrt{137}=2\sqrt{137}$
$x_{1}=\frac{-b-\sqrt{\Delta}}{2a}=\frac{-(-8)-2\sqrt{137}}{2*-1}=\frac{8-2\sqrt{137}}{-2}
$
$x_{2}=\frac{-b+\sqrt{\Delta}}{2a}=\frac{-(-8)+2\sqrt{137}}{2*-1}=\frac{8+2\sqrt{137}}{-2}
$