0=21x-4.9x^2-8

Solution for 0=21x-4.9x^2-8 equation:

0=21x-4.9x^2-8

We move all terms to the left:

0-(21x-4.9x^2-8)=0

We add all the numbers together, and all the variables

-(21x-4.9x^2-8)=0

We get rid of parentheses

4.9x^2-21x+8=0

a = 4.9; b = -21; c = +8;
Δ = b2-4ac
Δ = -212-4·4.9·8
Δ = 284.2
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{-(-21)-\sqrt{284.2}}{2*4.9}=\frac{21-\sqrt{284.2}}{9.8}
$
$x_{2}=\frac{-b+\sqrt{\Delta}}{2a}=\frac{-(-21)+\sqrt{284.2}}{2*4.9}=\frac{21+\sqrt{284.2}}{9.8}
$