(m-4)(5m+2)=0

Solution for (m-4)(5m+2)=0 equation:

(m-4)(5m+2)=0

We multiply parentheses ..

(+5m^2+2m-20m-8)=0

We get rid of parentheses

5m^2+2m-20m-8=0

We add all the numbers together, and all the variables

5m^2-18m-8=0

a = 5; b = -18; c = -8;
Δ = b2-4ac
Δ = -182-4·5·(-8)
Δ = 484
The delta value is higher than zero, so the equation has two solutions
We use following formulas to calculate our solutions:
$m_{1}=\frac{-b-\sqrt{\Delta}}{2a}$
$m_{2}=\frac{-b+\sqrt{\Delta}}{2a}$

$\sqrt{\Delta}=\sqrt{484}=22$
$m_{1}=\frac{-b-\sqrt{\Delta}}{2a}=\frac{-(-18)-22}{2*5}=\frac{-4}{10}
=-2/5
$
$m_{2}=\frac{-b+\sqrt{\Delta}}{2a}=\frac{-(-18)+22}{2*5}=\frac{40}{10}
=4
$