-4.9x^2+8x+20=0

Solution for -4.9x^2+8x+20=0 equation:

-4.9x^2+8x+20=0

a = -4.9; b = 8; c = +20;
Δ = b2-4ac
Δ = 82-4·(-4.9)·20
Δ = 456
The delta value is higher than zero, so the equation has two solutions
We use following formulas to calculate our solutions:
$x_{1}=\frac{-b-\sqrt{\Delta}}{2a}$
$x_{2}=\frac{-b+\sqrt{\Delta}}{2a}$

The end solution:

$\sqrt{\Delta}=\sqrt{456}=\sqrt{4*114}=\sqrt{4}*\sqrt{114}=2\sqrt{114}$
$x_{1}=\frac{-b-\sqrt{\Delta}}{2a}=\frac{-(8)-2\sqrt{114}}{2*-4.9}=\frac{-8-2\sqrt{114}}{-9.8}
$
$x_{2}=\frac{-b+\sqrt{\Delta}}{2a}=\frac{-(8)+2\sqrt{114}}{2*-4.9}=\frac{-8+2\sqrt{114}}{-9.8}
$