x^2+10x+25-4x(x+5)=0

Solution for x^2+10x+25-4x(x+5)=0 equation:

x^2+10x+25-4x(x+5)=0

We multiply parentheses

x^2-4x^2+10x-20x+25=0

We add all the numbers together, and all the variables

-3x^2-10x+25=0

a = -3; b = -10; c = +25;
Δ = b2-4ac
Δ = -102-4·(-3)·25
Δ = 400
The delta value is higher than zero, so the equation has two solutions
We use following formulas to calculate our solutions:
$x_{1}=\frac{-b-\sqrt{\Delta}}{2a}$
$x_{2}=\frac{-b+\sqrt{\Delta}}{2a}$

$\sqrt{\Delta}=\sqrt{400}=20$
$x_{1}=\frac{-b-\sqrt{\Delta}}{2a}=\frac{-(-10)-20}{2*-3}=\frac{-10}{-6}
=1+2/3
$
$x_{2}=\frac{-b+\sqrt{\Delta}}{2a}=\frac{-(-10)+20}{2*-3}=\frac{30}{-6}
=-5
$