4(5x-4)(7x+2)=0

Solution for 4(5x-4)(7x+2)=0 equation:

4(5x-4)(7x+2)=0

We multiply parentheses ..

4(+35x^2+10x-28x-8)=0

We multiply parentheses

140x^2+40x-112x-32=0

We add all the numbers together, and all the variables

140x^2-72x-32=0

a = 140; b = -72; c = -32;
Δ = b2-4ac
Δ = -722-4·140·(-32)
Δ = 23104
The delta value is higher than zero, so the equation has two solutions
We use following formulas to calculate our solutions:
$x_{1}=\frac{-b-\sqrt{\Delta}}{2a}$
$x_{2}=\frac{-b+\sqrt{\Delta}}{2a}$

$\sqrt{\Delta}=\sqrt{23104}=152$
$x_{1}=\frac{-b-\sqrt{\Delta}}{2a}=\frac{-(-72)-152}{2*140}=\frac{-80}{280}
=-2/7
$
$x_{2}=\frac{-b+\sqrt{\Delta}}{2a}=\frac{-(-72)+152}{2*140}=\frac{224}{280}
=4/5
$