X2-9x=100

Solution for X2-9x=100 equation:

X2-9X=100

We move all terms to the left:

X2-9X-(100)=0

We add all the numbers together, and all the variables

X^2-9X-100=0

a = 1; b = -9; c = -100;
Δ = b2-4ac
Δ = -92-4·1·(-100)
Δ = 481
The delta value is higher than zero, so the equation has two solutions
We use following formulas to calculate our solutions:
$X_{1}=\frac{-b-\sqrt{\Delta}}{2a}$
$X_{2}=\frac{-b+\sqrt{\Delta}}{2a}$

$X_{1}=\frac{-b-\sqrt{\Delta}}{2a}=\frac{-(-9)-\sqrt{481}}{2*1}=\frac{9-\sqrt{481}}{2}
$
$X_{2}=\frac{-b+\sqrt{\Delta}}{2a}=\frac{-(-9)+\sqrt{481}}{2*1}=\frac{9+\sqrt{481}}{2}
$