2b(7b-4)=0

Solution for 2b(7b-4)=0 equation:

2b(7b-4)=0

We multiply parentheses

14b^2-8b=0

a = 14; b = -8; c = 0;
Δ = b2-4ac
Δ = -82-4·14·0
Δ = 64
The delta value is higher than zero, so the equation has two solutions
We use following formulas to calculate our solutions:
$b_{1}=\frac{-b-\sqrt{\Delta}}{2a}$
$b_{2}=\frac{-b+\sqrt{\Delta}}{2a}$

$\sqrt{\Delta}=\sqrt{64}=8$
$b_{1}=\frac{-b-\sqrt{\Delta}}{2a}=\frac{-(-8)-8}{2*14}=\frac{0}{28}
=0
$
$b_{2}=\frac{-b+\sqrt{\Delta}}{2a}=\frac{-(-8)+8}{2*14}=\frac{16}{28}
=4/7
$