225=x^2+10x

Solution for 225=x^2+10x equation:

225=x^2+10x

We move all terms to the left:

225-(x^2+10x)=0

We get rid of parentheses

-x^2-10x+225=0

We add all the numbers together, and all the variables

-1x^2-10x+225=0

a = -1; b = -10; c = +225;
Δ = b2-4ac
Δ = -102-4·(-1)·225
Δ = 1000
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:

$\sqrt{\Delta}=\sqrt{1000}=\sqrt{100*10}=\sqrt{100}*\sqrt{10}=10\sqrt{10}$
$x_{1}=\frac{-b-\sqrt{\Delta}}{2a}=\frac{-(-10)-10\sqrt{10}}{2*-1}=\frac{10-10\sqrt{10}}{-2}
$
$x_{2}=\frac{-b+\sqrt{\Delta}}{2a}=\frac{-(-10)+10\sqrt{10}}{2*-1}=\frac{10+10\sqrt{10}}{-2}
$