9.8t^2-20t-4=0

Solution for 9.8t^2-20t-4=0 equation:

9.8t^2-20t-4=0

a = 9.8; b = -20; c = -4;
Δ = b2-4ac
Δ = -202-4·9.8·(-4)
Δ = 556.8
The delta value is higher than zero, so the equation has two solutions
We use following formulas to calculate our solutions:
$t_{1}=\frac{-b-\sqrt{\Delta}}{2a}$
$t_{2}=\frac{-b+\sqrt{\Delta}}{2a}$

$t_{1}=\frac{-b-\sqrt{\Delta}}{2a}=\frac{-(-20)-\sqrt{556.8}}{2*9.8}=\frac{20-\sqrt{556.8}}{19.6}
$
$t_{2}=\frac{-b+\sqrt{\Delta}}{2a}=\frac{-(-20)+\sqrt{556.8}}{2*9.8}=\frac{20+\sqrt{556.8}}{19.6}
$