3x(-7)(4x+9)=0

Solution for 3x(-7)(4x+9)=0 equation:

3x(-7)(4x+9)=0

We multiply parentheses ..

3x(-28x-63)=0

We multiply parentheses

-84x^2-189x=0

a = -84; b = -189; c = 0;
Δ = b2-4ac
Δ = -1892-4·(-84)·0
Δ = 35721
The delta value is higher than zero, so the equation has two solutions
We use following formulas to calculate our solutions:
$x_{1}=\frac{-b-\sqrt{\Delta}}{2a}$
$x_{2}=\frac{-b+\sqrt{\Delta}}{2a}$

$\sqrt{\Delta}=\sqrt{35721}=189$
$x_{1}=\frac{-b-\sqrt{\Delta}}{2a}=\frac{-(-189)-189}{2*-84}=\frac{0}{-168}
=0
$
$x_{2}=\frac{-b+\sqrt{\Delta}}{2a}=\frac{-(-189)+189}{2*-84}=\frac{378}{-168}
=-2+1/4
$