1.8=2.25x+4.9x^2

Solution for 1.8=2.25x+4.9x^2 equation:

1.8=2.25x+4.9x^2

We move all terms to the left:

1.8-(2.25x+4.9x^2)=0

We get rid of parentheses

-4.9x^2-2.25x+1.8=0

a = -4.9; b = -2.25; c = +1.8;
Δ = b2-4ac
Δ = -2.252-4·(-4.9)·1.8
Δ = 40.3425
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{-(-2.25)-\sqrt{40.3425}}{2*-4.9}=\frac{2.25-\sqrt{40.3425}}{-9.8}
$
$x_{2}=\frac{-b+\sqrt{\Delta}}{2a}=\frac{-(-2.25)+\sqrt{40.3425}}{2*-4.9}=\frac{2.25+\sqrt{40.3425}}{-9.8}
$