3x(-7x-8)=0

Solution for 3x(-7x-8)=0 equation:

3x(-7x-8)=0

We multiply parentheses

-21x^2-24x=0

a = -21; b = -24; c = 0;
Δ = b2-4ac
Δ = -242-4·(-21)·0
Δ = 576
The delta value is higher than zero, so the equation has two solutions
We use following formulas to calculate our solutions:
$x_{1}=\frac{-b-\sqrt{\Delta}}{2a}$
$x_{2}=\frac{-b+\sqrt{\Delta}}{2a}$

$\sqrt{\Delta}=\sqrt{576}=24$
$x_{1}=\frac{-b-\sqrt{\Delta}}{2a}=\frac{-(-24)-24}{2*-21}=\frac{0}{-42}
=0
$
$x_{2}=\frac{-b+\sqrt{\Delta}}{2a}=\frac{-(-24)+24}{2*-21}=\frac{48}{-42}
=-1+1/7
$