-4.9t(t+5)=0

Solution for -4.9t(t+5)=0 equation:

-4.9t(t+5)=0

We multiply parentheses

-4t^2-20t=0

a = -4; b = -20; c = 0;
Δ = b2-4ac
Δ = -202-4·(-4)·0
Δ = 400
The delta value is higher than zero, so the equation has two solutions
We use following formulas to calculate our solutions:
$t_{1}=\frac{-b-\sqrt{\Delta}}{2a}$
$t_{2}=\frac{-b+\sqrt{\Delta}}{2a}$

$\sqrt{\Delta}=\sqrt{400}=20$
$t_{1}=\frac{-b-\sqrt{\Delta}}{2a}=\frac{-(-20)-20}{2*-4}=\frac{0}{-8}
=0
$
$t_{2}=\frac{-b+\sqrt{\Delta}}{2a}=\frac{-(-20)+20}{2*-4}=\frac{40}{-8}
=-5
$