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

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

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

a = -5; b = -15; c = +20;
Δ = b2-4ac
Δ = -152-4·(-5)·20
Δ = 625
The delta value is higher than zero, so the equation has two solutions
We use following formulas to calculate our solutions:
$x_{1}=\frac{-b-\sqrt{\Delta}}{2a}$
$x_{2}=\frac{-b+\sqrt{\Delta}}{2a}$

$\sqrt{\Delta}=\sqrt{625}=25$
$x_{1}=\frac{-b-\sqrt{\Delta}}{2a}=\frac{-(-15)-25}{2*-5}=\frac{-10}{-10}
=1
$
$x_{2}=\frac{-b+\sqrt{\Delta}}{2a}=\frac{-(-15)+25}{2*-5}=\frac{40}{-10}
=-4
$