1.2x(x+8.4)=0.3x

Solution for 1.2x(x+8.4)=0.3x equation:

1.2x(x+8.4)=0.3x

We move all terms to the left:

1.2x(x+8.4)-(0.3x)=0

We add all the numbers together, and all the variables

1.2x(x+8.4)-(+0.3x)=0

We multiply parentheses

x^2+8.4x-(+0.3x)=0

We get rid of parentheses

x^2+8.4x-0.3x=0

We add all the numbers together, and all the variables

x^2+8.1x=0

a = 1; b = 8.1; c = 0;
Δ = b2-4ac
Δ = 8.12-4·1·0
Δ = 65.61
The delta value is higher than zero, so the equation has two solutions
We use following formulas to calculate our solutions:
$x_{1}=\frac{-b-\sqrt{\Delta}}{2a}$
$x_{2}=\frac{-b+\sqrt{\Delta}}{2a}$

$x_{1}=\frac{-b-\sqrt{\Delta}}{2a}=\frac{-(8.1)-\sqrt{65.61}}{2*1}=\frac{-8.1-\sqrt{65.61}}{2}
$
$x_{2}=\frac{-b+\sqrt{\Delta}}{2a}=\frac{-(8.1)+\sqrt{65.61}}{2*1}=\frac{-8.1+\sqrt{65.61}}{2}
$