x(0.2x)=55

Solution for x(0.2x)=55 equation:

x(0.2x)=55

We move all terms to the left:

x(0.2x)-(55)=0

We add all the numbers together, and all the variables

x(+0.2x)-55=0

We multiply parentheses

0x^2-55=0

We add all the numbers together, and all the variables

x^2-55=0

a = 1; b = 0; c = -55;
Δ = b2-4ac
Δ = 02-4·1·(-55)
Δ = 220
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:

$\sqrt{\Delta}=\sqrt{220}=\sqrt{4*55}=\sqrt{4}*\sqrt{55}=2\sqrt{55}$
$x_{1}=\frac{-b-\sqrt{\Delta}}{2a}=\frac{-(0)-2\sqrt{55}}{2*1}=\frac{0-2\sqrt{55}}{2}
=-\frac{2\sqrt{55}}{2}
=-\sqrt{55}
$
$x_{2}=\frac{-b+\sqrt{\Delta}}{2a}=\frac{-(0)+2\sqrt{55}}{2*1}=\frac{0+2\sqrt{55}}{2}
=\frac{2\sqrt{55}}{2}
=\sqrt{55}
$