2x(4x+3x)=21

Solution for 2x(4x+3x)=21 equation:

2x(4x+3x)=21

We move all terms to the left:

2x(4x+3x)-(21)=0

We add all the numbers together, and all the variables

2x(+7x)-21=0

We multiply parentheses

14x^2-21=0

a = 14; b = 0; c = -21;
Δ = b2-4ac
Δ = 02-4·14·(-21)
Δ = 1176
The delta value is higher than zero, so the equation has two solutions
We use following formulas to calculate our solutions:
$x_{1}=\frac{-b-\sqrt{\Delta}}{2a}$
$x_{2}=\frac{-b+\sqrt{\Delta}}{2a}$

The end solution:

$\sqrt{\Delta}=\sqrt{1176}=\sqrt{196*6}=\sqrt{196}*\sqrt{6}=14\sqrt{6}$
$x_{1}=\frac{-b-\sqrt{\Delta}}{2a}=\frac{-(0)-14\sqrt{6}}{2*14}=\frac{0-14\sqrt{6}}{28}
=-\frac{14\sqrt{6}}{28}
=-\frac{\sqrt{6}}{2}
$
$x_{2}=\frac{-b+\sqrt{\Delta}}{2a}=\frac{-(0)+14\sqrt{6}}{2*14}=\frac{0+14\sqrt{6}}{28}
=\frac{14\sqrt{6}}{28}
=\frac{\sqrt{6}}{2}
$