x(x+5)=90

Solution for x(x+5)=90 equation:

x(x+5)=90

We move all terms to the left:

x(x+5)-(90)=0

We multiply parentheses

x^2+5x-90=0

a = 1; b = 5; c = -90;
Δ = b2-4ac
Δ = 52-4·1·(-90)
Δ = 385
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{-(5)-\sqrt{385}}{2*1}=\frac{-5-\sqrt{385}}{2}
$
$x_{2}=\frac{-b+\sqrt{\Delta}}{2a}=\frac{-(5)+\sqrt{385}}{2*1}=\frac{-5+\sqrt{385}}{2}
$