490=8x+2x^2

Solution for 490=8x+2x^2 equation:

490=8x+2x^2

We move all terms to the left:

490-(8x+2x^2)=0

We get rid of parentheses

-2x^2-8x+490=0

a = -2; b = -8; c = +490;
Δ = b2-4ac
Δ = -82-4·(-2)·490
Δ = 3984
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:

$\sqrt{\Delta}=\sqrt{3984}=\sqrt{16*249}=\sqrt{16}*\sqrt{249}=4\sqrt{249}$
$x_{1}=\frac{-b-\sqrt{\Delta}}{2a}=\frac{-(-8)-4\sqrt{249}}{2*-2}=\frac{8-4\sqrt{249}}{-4}
$
$x_{2}=\frac{-b+\sqrt{\Delta}}{2a}=\frac{-(-8)+4\sqrt{249}}{2*-2}=\frac{8+4\sqrt{249}}{-4}
$