x2+20x-100=225

Solution for x2+20x-100=225 equation:

x2+20x-100=225

We move all terms to the left:

x2+20x-100-(225)=0

We add all the numbers together, and all the variables

x^2+20x-325=0

a = 1; b = 20; c = -325;
Δ = b2-4ac
Δ = 202-4·1·(-325)
Δ = 1700
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:

$\sqrt{\Delta}=\sqrt{1700}=\sqrt{100*17}=\sqrt{100}*\sqrt{17}=10\sqrt{17}$
$x_{1}=\frac{-b-\sqrt{\Delta}}{2a}=\frac{-(20)-10\sqrt{17}}{2*1}=\frac{-20-10\sqrt{17}}{2}
$
$x_{2}=\frac{-b+\sqrt{\Delta}}{2a}=\frac{-(20)+10\sqrt{17}}{2*1}=\frac{-20+10\sqrt{17}}{2}
$