84=x^2+x-6

Solution for 84=x^2+x-6 equation:

84=x^2+x-6

We move all terms to the left:

84-(x^2+x-6)=0

We get rid of parentheses

-x^2-x+6+84=0

We add all the numbers together, and all the variables

-1x^2-1x+90=0

a = -1; b = -1; c = +90;
Δ = b2-4ac
Δ = -12-4·(-1)·90
Δ = 361
The delta value is higher than zero, so the equation has two solutions
We use following formulas to calculate our solutions:
$x_{1}=\frac{-b-\sqrt{\Delta}}{2a}$
$x_{2}=\frac{-b+\sqrt{\Delta}}{2a}$

$\sqrt{\Delta}=\sqrt{361}=19$
$x_{1}=\frac{-b-\sqrt{\Delta}}{2a}=\frac{-(-1)-19}{2*-1}=\frac{-18}{-2}
=+9
$
$x_{2}=\frac{-b+\sqrt{\Delta}}{2a}=\frac{-(-1)+19}{2*-1}=\frac{20}{-2}
=-10
$