100=x^2-6x

Solution for 100=x^2-6x equation:

100=x^2-6x

We move all terms to the left:

100-(x^2-6x)=0

We get rid of parentheses

-x^2+6x+100=0

We add all the numbers together, and all the variables

-1x^2+6x+100=0

a = -1; b = 6; c = +100;
Δ = b2-4ac
Δ = 62-4·(-1)·100
Δ = 436
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:

$\sqrt{\Delta}=\sqrt{436}=\sqrt{4*109}=\sqrt{4}*\sqrt{109}=2\sqrt{109}$
$x_{1}=\frac{-b-\sqrt{\Delta}}{2a}=\frac{-(6)-2\sqrt{109}}{2*-1}=\frac{-6-2\sqrt{109}}{-2}
$
$x_{2}=\frac{-b+\sqrt{\Delta}}{2a}=\frac{-(6)+2\sqrt{109}}{2*-1}=\frac{-6+2\sqrt{109}}{-2}
$