-5s^2+20s-15=0

Solution for -5s^2+20s-15=0 equation:

-5s^2+20s-15=0

a = -5; b = 20; c = -15;
Δ = b2-4ac
Δ = 202-4·(-5)·(-15)
Δ = 100
The delta value is higher than zero, so the equation has two solutions
We use following formulas to calculate our solutions:
$s_{1}=\frac{-b-\sqrt{\Delta}}{2a}$
$s_{2}=\frac{-b+\sqrt{\Delta}}{2a}$

$\sqrt{\Delta}=\sqrt{100}=10$
$s_{1}=\frac{-b-\sqrt{\Delta}}{2a}=\frac{-(20)-10}{2*-5}=\frac{-30}{-10}
=+3
$
$s_{2}=\frac{-b+\sqrt{\Delta}}{2a}=\frac{-(20)+10}{2*-5}=\frac{-10}{-10}
=1
$