x*2x=84

Solution for x*2x=84 equation:

x*2x=84

We move all terms to the left:

x*2x-(84)=0

Wy multiply elements

2x^2-84=0

a = 2; b = 0; c = -84;
Δ = b2-4ac
Δ = 02-4·2·(-84)
Δ = 672
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:

$\sqrt{\Delta}=\sqrt{672}=\sqrt{16*42}=\sqrt{16}*\sqrt{42}=4\sqrt{42}$
$x_{1}=\frac{-b-\sqrt{\Delta}}{2a}=\frac{-(0)-4\sqrt{42}}{2*2}=\frac{0-4\sqrt{42}}{4}
=-\frac{4\sqrt{42}}{4}
=-\sqrt{42}
$
$x_{2}=\frac{-b+\sqrt{\Delta}}{2a}=\frac{-(0)+4\sqrt{42}}{2*2}=\frac{0+4\sqrt{42}}{4}
=\frac{4\sqrt{42}}{4}
=\sqrt{42}
$