4x*5x=8.4

Solution for 4x*5x=8.4 equation:

4x*5x=8.4

We move all terms to the left:

4x*5x-(8.4)=0

We add all the numbers together, and all the variables

4x*5x-8.4=0

Wy multiply elements

20x^2-8.4=0

a = 20; b = 0; c = -8.4;
Δ = b2-4ac
Δ = 02-4·20·(-8.4)
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*20}=\frac{0-4\sqrt{42}}{40}
=-\frac{4\sqrt{42}}{40}
=-\frac{\sqrt{42}}{10}
$
$x_{2}=\frac{-b+\sqrt{\Delta}}{2a}=\frac{-(0)+4\sqrt{42}}{2*20}=\frac{0+4\sqrt{42}}{40}
=\frac{4\sqrt{42}}{40}
=\frac{\sqrt{42}}{10}
$