x^2+5x+8+2x^2+x-4=90

Solution for x^2+5x+8+2x^2+x-4=90 equation:

x^2+5x+8+2x^2+x-4=90

We move all terms to the left:

x^2+5x+8+2x^2+x-4-(90)=0

We add all the numbers together, and all the variables

3x^2+6x-86=0

a = 3; b = 6; c = -86;
Δ = b2-4ac
Δ = 62-4·3·(-86)
Δ = 1068
The delta value is higher than zero, so the equation has two solutions
We use following formulas to calculate our solutions:
$x_{1}=\frac{-b-\sqrt{\Delta}}{2a}$
$x_{2}=\frac{-b+\sqrt{\Delta}}{2a}$

The end solution:

$\sqrt{\Delta}=\sqrt{1068}=\sqrt{4*267}=\sqrt{4}*\sqrt{267}=2\sqrt{267}$
$x_{1}=\frac{-b-\sqrt{\Delta}}{2a}=\frac{-(6)-2\sqrt{267}}{2*3}=\frac{-6-2\sqrt{267}}{6}
$
$x_{2}=\frac{-b+\sqrt{\Delta}}{2a}=\frac{-(6)+2\sqrt{267}}{2*3}=\frac{-6+2\sqrt{267}}{6}
$