(10x+5)(-x-2)=0

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

(10x+5)(-x-2)=0

We add all the numbers together, and all the variables

(10x+5)(-1x-2)=0

We multiply parentheses ..

(-10x^2-20x-5x-10)=0

We get rid of parentheses

-10x^2-20x-5x-10=0

We add all the numbers together, and all the variables

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

a = -10; b = -25; c = -10;
Δ = b2-4ac
Δ = -252-4·(-10)·(-10)
Δ = 225
The delta value is higher than zero, so the equation has two solutions
We use following formulas to calculate our solutions:
$x_{1}=\frac{-b-\sqrt{\Delta}}{2a}$
$x_{2}=\frac{-b+\sqrt{\Delta}}{2a}$

$\sqrt{\Delta}=\sqrt{225}=15$
$x_{1}=\frac{-b-\sqrt{\Delta}}{2a}=\frac{-(-25)-15}{2*-10}=\frac{10}{-20}
=-1/2
$
$x_{2}=\frac{-b+\sqrt{\Delta}}{2a}=\frac{-(-25)+15}{2*-10}=\frac{40}{-20}
=-2
$