8x^2+18=90

Solution for 8x^2+18=90 equation:

8x^2+18=90

We move all terms to the left:

8x^2+18-(90)=0

We add all the numbers together, and all the variables

8x^2-72=0

a = 8; b = 0; c = -72;
Δ = b2-4ac
Δ = 02-4·8·(-72)
Δ = 2304
The delta value is higher than zero, so the equation has two solutions
We use following formulas to calculate our solutions:
$x_{1}=\frac{-b-\sqrt{\Delta}}{2a}$
$x_{2}=\frac{-b+\sqrt{\Delta}}{2a}$

$\sqrt{\Delta}=\sqrt{2304}=48$
$x_{1}=\frac{-b-\sqrt{\Delta}}{2a}=\frac{-(0)-48}{2*8}=\frac{-48}{16}
=-3
$
$x_{2}=\frac{-b+\sqrt{\Delta}}{2a}=\frac{-(0)+48}{2*8}=\frac{48}{16}
=3
$