-5f^2-18f+8=0

Solution for -5f^2-18f+8=0 equation:

-5f^2-18f+8=0

a = -5; b = -18; c = +8;
Δ = b2-4ac
Δ = -182-4·(-5)·8
Δ = 484
The delta value is higher than zero, so the equation has two solutions
We use following formulas to calculate our solutions:
$f_{1}=\frac{-b-\sqrt{\Delta}}{2a}$
$f_{2}=\frac{-b+\sqrt{\Delta}}{2a}$

$\sqrt{\Delta}=\sqrt{484}=22$
$f_{1}=\frac{-b-\sqrt{\Delta}}{2a}=\frac{-(-18)-22}{2*-5}=\frac{-4}{-10}
=2/5
$
$f_{2}=\frac{-b+\sqrt{\Delta}}{2a}=\frac{-(-18)+22}{2*-5}=\frac{40}{-10}
=-4
$