-4=-4.905t^2

Solution for -4=-4.905t^2 equation:

-4=-4.905t^2

We move all terms to the left:

-4-(-4.905t^2)=0

We get rid of parentheses

4.905t^2-4=0

a = 4.905; b = 0; c = -4;
Δ = b2-4ac
Δ = 02-4·4.905·(-4)
Δ = 78.48
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{-(0)-\sqrt{78.48}}{2*4.905}=\frac{0-\sqrt{78.48}}{9.81}
=-\frac{\sqrt{}}{9.81}
$
$t_{2}=\frac{-b+\sqrt{\Delta}}{2a}=\frac{-(0)+\sqrt{78.48}}{2*4.905}=\frac{0+\sqrt{78.48}}{9.81}
=\frac{\sqrt{}}{9.81}
$