0.8=x+4.9x^2

Solution for 0.8=x+4.9x^2 equation:

0.8=x+4.9x^2

We move all terms to the left:

0.8-(x+4.9x^2)=0

We get rid of parentheses

-4.9x^2-x+0.8=0

We add all the numbers together, and all the variables

-4.9x^2-1x+0.8=0

a = -4.9; b = -1; c = +0.8;
Δ = b2-4ac
Δ = -12-4·(-4.9)·0.8
Δ = 16.68
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{16.68}}{2*-4.9}=\frac{1-\sqrt{16.68}}{-9.8}
$
$x_{2}=\frac{-b+\sqrt{\Delta}}{2a}=\frac{-(-1)+\sqrt{16.68}}{2*-4.9}=\frac{1+\sqrt{16.68}}{-9.8}
$