x(x+1)=13.64

Solution for x(x+1)=13.64 equation:

x(x+1)=13.64

We move all terms to the left:

x(x+1)-(13.64)=0

We add all the numbers together, and all the variables

x(x+1)-13.64=0

We multiply parentheses

x^2+x-13.64=0

a = 1; b = 1; c = -13.64;
Δ = b2-4ac
Δ = 12-4·1·(-13.64)
Δ = 55.56
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{-(1)-\sqrt{55.56}}{2*1}=\frac{-1-\sqrt{55.56}}{2}
$
$x_{2}=\frac{-b+\sqrt{\Delta}}{2a}=\frac{-(1)+\sqrt{55.56}}{2*1}=\frac{-1+\sqrt{55.56}}{2}
$