(b+8)(5b-4)=0

Solution for (b+8)(5b-4)=0 equation:

(b+8)(5b-4)=0

We multiply parentheses ..

(+5b^2-4b+40b-32)=0

We get rid of parentheses

5b^2-4b+40b-32=0

We add all the numbers together, and all the variables

5b^2+36b-32=0

a = 5; b = 36; c = -32;
Δ = b2-4ac
Δ = 362-4·5·(-32)
Δ = 1936
The delta value is higher than zero, so the equation has two solutions
We use following formulas to calculate our solutions:
$b_{1}=\frac{-b-\sqrt{\Delta}}{2a}$
$b_{2}=\frac{-b+\sqrt{\Delta}}{2a}$

$\sqrt{\Delta}=\sqrt{1936}=44$
$b_{1}=\frac{-b-\sqrt{\Delta}}{2a}=\frac{-(36)-44}{2*5}=\frac{-80}{10}
=-8
$
$b_{2}=\frac{-b+\sqrt{\Delta}}{2a}=\frac{-(36)+44}{2*5}=\frac{8}{10}
=4/5
$