-16t^2-8t+20=0

Solution for -16t^2-8t+20=0 equation:

-16t^2-8t+20=0

a = -16; b = -8; c = +20;
Δ = b2-4ac
Δ = -82-4·(-16)·20
Δ = 1344
The delta value is higher than zero, so the equation has two solutions
We use following formulas to calculate our solutions:
$t_{1}=\frac{-b-\sqrt{\Delta}}{2a}$
$t_{2}=\frac{-b+\sqrt{\Delta}}{2a}$

The end solution:

$\sqrt{\Delta}=\sqrt{1344}=\sqrt{64*21}=\sqrt{64}*\sqrt{21}=8\sqrt{21}$
$t_{1}=\frac{-b-\sqrt{\Delta}}{2a}=\frac{-(-8)-8\sqrt{21}}{2*-16}=\frac{8-8\sqrt{21}}{-32}
$
$t_{2}=\frac{-b+\sqrt{\Delta}}{2a}=\frac{-(-8)+8\sqrt{21}}{2*-16}=\frac{8+8\sqrt{21}}{-32}
$