-4.9t^2+55t-2.8=0

Solution for -4.9t^2+55t-2.8=0 equation:

-4.9t^2+55t-2.8=0

a = -4.9; b = 55; c = -2.8;
Δ = b2-4ac
Δ = 552-4·(-4.9)·(-2.8)
Δ = 2970.12
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{-(55)-\sqrt{2970.12}}{2*-4.9}=\frac{-55-\sqrt{2970.12}}{-9.8}
$
$t_{2}=\frac{-b+\sqrt{\Delta}}{2a}=\frac{-(55)+\sqrt{2970.12}}{2*-4.9}=\frac{-55+\sqrt{2970.12}}{-9.8}
$