2.6=20x-4.9x^2

Solution for 2.6=20x-4.9x^2 equation:

2.6=20x-4.9x^2

We move all terms to the left:

2.6-(20x-4.9x^2)=0

We get rid of parentheses

4.9x^2-20x+2.6=0

a = 4.9; b = -20; c = +2.6;
Δ = b2-4ac
Δ = -202-4·4.9·2.6
Δ = 349.04
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{-(-20)-\sqrt{349.04}}{2*4.9}=\frac{20-\sqrt{349.04}}{9.8}
$
$x_{2}=\frac{-b+\sqrt{\Delta}}{2a}=\frac{-(-20)+\sqrt{349.04}}{2*4.9}=\frac{20+\sqrt{349.04}}{9.8}
$