x*x*(0.04x+55)=1380

Solution for x*x*(0.04x+55)=1380 equation:

x*x(0.04x+55)=1380

We move all terms to the left:

x*x(0.04x+55)-(1380)=0

Wy multiply elements

x^2-1380=0

a = 1; b = 0; c = -1380;
Δ = b2-4ac
Δ = 02-4·1·(-1380)
Δ = 5520
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:

$\sqrt{\Delta}=\sqrt{5520}=\sqrt{16*345}=\sqrt{16}*\sqrt{345}=4\sqrt{345}$
$x_{1}=\frac{-b-\sqrt{\Delta}}{2a}=\frac{-(0)-4\sqrt{345}}{2*1}=\frac{0-4\sqrt{345}}{2}
=-\frac{4\sqrt{345}}{2}
=-2\sqrt{345}
$
$x_{2}=\frac{-b+\sqrt{\Delta}}{2a}=\frac{-(0)+4\sqrt{345}}{2*1}=\frac{0+4\sqrt{345}}{2}
=\frac{4\sqrt{345}}{2}
=2\sqrt{345}
$