X2-3x=100

Solution for X2-3x=100 equation:

X2-3X=100

We move all terms to the left:

X2-3X-(100)=0

We add all the numbers together, and all the variables

X^2-3X-100=0

a = 1; b = -3; c = -100;
Δ = b2-4ac
Δ = -32-4·1·(-100)
Δ = 409
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{-(-3)-\sqrt{409}}{2*1}=\frac{3-\sqrt{409}}{2}
$
$X_{2}=\frac{-b+\sqrt{\Delta}}{2a}=\frac{-(-3)+\sqrt{409}}{2*1}=\frac{3+\sqrt{409}}{2}
$