0=-4.9x^2+2x+21

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

0=-4.9x^2+2x+21

We move all terms to the left:

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

We add all the numbers together, and all the variables

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

We get rid of parentheses

4.9x^2-2x-21=0

a = 4.9; b = -2; c = -21;
Δ = b2-4ac
Δ = -22-4·4.9·(-21)
Δ = 415.6
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)-\sqrt{415.6}}{2*4.9}=\frac{2-\sqrt{415.6}}{9.8}
$
$x_{2}=\frac{-b+\sqrt{\Delta}}{2a}=\frac{-(-2)+\sqrt{415.6}}{2*4.9}=\frac{2+\sqrt{415.6}}{9.8}
$