(2x+2x)x=84

Solution for (2x+2x)x=84 equation:

(2x+2x)x=84

We move all terms to the left:

(2x+2x)x-(84)=0

We add all the numbers together, and all the variables

(+4x)x-84=0

We multiply parentheses

4x^2-84=0

a = 4; b = 0; c = -84;
Δ = b2-4ac
Δ = 02-4·4·(-84)
Δ = 1344
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:

$\sqrt{\Delta}=\sqrt{1344}=\sqrt{64*21}=\sqrt{64}*\sqrt{21}=8\sqrt{21}$
$x_{1}=\frac{-b-\sqrt{\Delta}}{2a}=\frac{-(0)-8\sqrt{21}}{2*4}=\frac{0-8\sqrt{21}}{8}
=-\frac{8\sqrt{21}}{8}
=-\sqrt{21}
$
$x_{2}=\frac{-b+\sqrt{\Delta}}{2a}=\frac{-(0)+8\sqrt{21}}{2*4}=\frac{0+8\sqrt{21}}{8}
=\frac{8\sqrt{21}}{8}
=\sqrt{21}
$