x(x=90)

Solution for x(x=90) equation:

x(x=90)

We move all terms to the left:

x(x-(90))=0

We multiply parentheses

x^2-90x=0

a = 1; b = -90; c = 0;
Δ = b2-4ac
Δ = -902-4·1·0
Δ = 8100
The delta value is higher than zero, so the equation has two solutions
We use following formulas to calculate our solutions:
$x_{1}=\frac{-b-\sqrt{\Delta}}{2a}$
$x_{2}=\frac{-b+\sqrt{\Delta}}{2a}$

$\sqrt{\Delta}=\sqrt{8100}=90$
$x_{1}=\frac{-b-\sqrt{\Delta}}{2a}=\frac{-(-90)-90}{2*1}=\frac{0}{2}
=0
$
$x_{2}=\frac{-b+\sqrt{\Delta}}{2a}=\frac{-(-90)+90}{2*1}=\frac{180}{2}
=90
$