(5x-40)(x+10)=0

Solution for (5x-40)(x+10)=0 equation:

(5x-40)(x+10)=0

We multiply parentheses ..

(+5x^2+50x-40x-400)=0

We get rid of parentheses

5x^2+50x-40x-400=0

We add all the numbers together, and all the variables

5x^2+10x-400=0

a = 5; b = 10; c = -400;
Δ = b2-4ac
Δ = 102-4·5·(-400)
Δ = 8100
The delta value is higher than zero, so the equation has two solutions
We use following formulas to calculate our solutions:
$x_{1}=\frac{-b-\sqrt{\Delta}}{2a}$
$x_{2}=\frac{-b+\sqrt{\Delta}}{2a}$

$\sqrt{\Delta}=\sqrt{8100}=90$
$x_{1}=\frac{-b-\sqrt{\Delta}}{2a}=\frac{-(10)-90}{2*5}=\frac{-100}{10}
=-10
$
$x_{2}=\frac{-b+\sqrt{\Delta}}{2a}=\frac{-(10)+90}{2*5}=\frac{80}{10}
=8
$