x(x+0.9)=0.36

Solution for x(x+0.9)=0.36 equation:

x(x+0.9)=0.36

We move all terms to the left:

x(x+0.9)-(0.36)=0

We add all the numbers together, and all the variables

x(x+0.9)-0.36=0

We multiply parentheses

x^2+0.9x-0.36=0

a = 1; b = 0.9; c = -0.36;
Δ = b2-4ac
Δ = 0.92-4·1·(-0.36)
Δ = 2.25
The delta value is higher than zero, so the equation has two solutions
We use following formulas to calculate our solutions:
$x_{1}=\frac{-b-\sqrt{\Delta}}{2a}$
$x_{2}=\frac{-b+\sqrt{\Delta}}{2a}$

$x_{1}=\frac{-b-\sqrt{\Delta}}{2a}=\frac{-(0.9)-\sqrt{2.25}}{2*1}=\frac{-0.9-\sqrt{2.25}}{2}
$
$x_{2}=\frac{-b+\sqrt{\Delta}}{2a}=\frac{-(0.9)+\sqrt{2.25}}{2*1}=\frac{-0.9+\sqrt{2.25}}{2}
$