-18=-4.7-4.9t^2

Solution for -18=-4.7-4.9t^2 equation:

-18=-4.7-4.9t^2

We move all terms to the left:

-18-(-4.7-4.9t^2)=0

We get rid of parentheses

4.9t^2+4.7-18=0

We add all the numbers together, and all the variables

4.9t^2-13.3=0

a = 4.9; b = 0; c = -13.3;
Δ = b2-4ac
Δ = 02-4·4.9·(-13.3)
Δ = 260.68
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{260.68}}{2*4.9}=\frac{0-\sqrt{260.68}}{9.8}
=-\frac{\sqrt{}}{9.8}
$
$t_{2}=\frac{-b+\sqrt{\Delta}}{2a}=\frac{-(0)+\sqrt{260.68}}{2*4.9}=\frac{0+\sqrt{260.68}}{9.8}
=\frac{\sqrt{}}{9.8}
$