(x-5)(-x-5)=0

Solution for (x-5)(-x-5)=0 equation:

(x-5)(-x-5)=0

We add all the numbers together, and all the variables

(x-5)(-1x-5)=0

We multiply parentheses ..

(-1x^2-5x+5x+25)=0

We get rid of parentheses

-1x^2-5x+5x+25=0

We add all the numbers together, and all the variables

-1x^2+25=0

a = -1; b = 0; c = +25;
Δ = b2-4ac
Δ = 02-4·(-1)·25
Δ = 100
The delta value is higher than zero, so the equation has two solutions
We use following formulas to calculate our solutions:
$x_{1}=\frac{-b-\sqrt{\Delta}}{2a}$
$x_{2}=\frac{-b+\sqrt{\Delta}}{2a}$

$\sqrt{\Delta}=\sqrt{100}=10$
$x_{1}=\frac{-b-\sqrt{\Delta}}{2a}=\frac{-(0)-10}{2*-1}=\frac{-10}{-2}
=+5
$
$x_{2}=\frac{-b+\sqrt{\Delta}}{2a}=\frac{-(0)+10}{2*-1}=\frac{10}{-2}
=-5
$