20r^2-17r-10=0

Solution for 20r^2-17r-10=0 equation:

20r^2-17r-10=0

a = 20; b = -17; c = -10;
Δ = b2-4ac
Δ = -172-4·20·(-10)
Δ = 1089
The delta value is higher than zero, so the equation has two solutions
We use following formulas to calculate our solutions:
$r_{1}=\frac{-b-\sqrt{\Delta}}{2a}$
$r_{2}=\frac{-b+\sqrt{\Delta}}{2a}$

$\sqrt{\Delta}=\sqrt{1089}=33$
$r_{1}=\frac{-b-\sqrt{\Delta}}{2a}=\frac{-(-17)-33}{2*20}=\frac{-16}{40}
=-2/5
$
$r_{2}=\frac{-b+\sqrt{\Delta}}{2a}=\frac{-(-17)+33}{2*20}=\frac{50}{40}
=1+1/4
$