-3x(7-2x)=0

Solution for -3x(7-2x)=0 equation:

-3x(7-2x)=0

We add all the numbers together, and all the variables

-3x(-2x+7)=0

We multiply parentheses

6x^2-21x=0

a = 6; b = -21; c = 0;
Δ = b2-4ac
Δ = -212-4·6·0
Δ = 441
The delta value is higher than zero, so the equation has two solutions
We use following formulas to calculate our solutions:
$x_{1}=\frac{-b-\sqrt{\Delta}}{2a}$
$x_{2}=\frac{-b+\sqrt{\Delta}}{2a}$

$\sqrt{\Delta}=\sqrt{441}=21$
$x_{1}=\frac{-b-\sqrt{\Delta}}{2a}=\frac{-(-21)-21}{2*6}=\frac{0}{12}
=0
$
$x_{2}=\frac{-b+\sqrt{\Delta}}{2a}=\frac{-(-21)+21}{2*6}=\frac{42}{12}
=3+1/2
$