90=x^2-x+8

Solution for 90=x^2-x+8 equation:

90=x^2-x+8

We move all terms to the left:

90-(x^2-x+8)=0

We get rid of parentheses

-x^2+x-8+90=0

We add all the numbers together, and all the variables

-1x^2+x+82=0

a = -1; b = 1; c = +82;
Δ = b2-4ac
Δ = 12-4·(-1)·82
Δ = 329
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{329}}{2*-1}=\frac{-1-\sqrt{329}}{-2}
$
$x_{2}=\frac{-b+\sqrt{\Delta}}{2a}=\frac{-(1)+\sqrt{329}}{2*-1}=\frac{-1+\sqrt{329}}{-2}
$