4+8t-5t^2=0

Solution for 4+8t-5t^2=0 equation:

4+8t-5t^2=0

a = -5; b = 8; c = +4;
Δ = b2-4ac
Δ = 82-4·(-5)·4
Δ = 144
The delta value is higher than zero, so the equation has two solutions
We use following formulas to calculate our solutions:
$t_{1}=\frac{-b-\sqrt{\Delta}}{2a}$
$t_{2}=\frac{-b+\sqrt{\Delta}}{2a}$

$\sqrt{\Delta}=\sqrt{144}=12$
$t_{1}=\frac{-b-\sqrt{\Delta}}{2a}=\frac{-(8)-12}{2*-5}=\frac{-20}{-10}
=+2
$
$t_{2}=\frac{-b+\sqrt{\Delta}}{2a}=\frac{-(8)+12}{2*-5}=\frac{4}{-10}
=-2/5
$