12x+4x(2)=840

Solution for 12x+4x(2)=840 equation:

12x+4x(2)=840

We move all terms to the left:

12x+4x(2)-(840)=0

We add all the numbers together, and all the variables

4x^2+12x-840=0

a = 4; b = 12; c = -840;
Δ = b2-4ac
Δ = 122-4·4·(-840)
Δ = 13584
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:

$\sqrt{\Delta}=\sqrt{13584}=\sqrt{16*849}=\sqrt{16}*\sqrt{849}=4\sqrt{849}$
$x_{1}=\frac{-b-\sqrt{\Delta}}{2a}=\frac{-(12)-4\sqrt{849}}{2*4}=\frac{-12-4\sqrt{849}}{8}
$
$x_{2}=\frac{-b+\sqrt{\Delta}}{2a}=\frac{-(12)+4\sqrt{849}}{2*4}=\frac{-12+4\sqrt{849}}{8}
$