8r^2-23r-36=0

Solution for 8r^2-23r-36=0 equation:

8r^2-23r-36=0

a = 8; b = -23; c = -36;
Δ = b2-4ac
Δ = -232-4·8·(-36)
Δ = 1681
The delta value is higher than zero, so the equation has two solutions
We use following formulas to calculate our solutions:
$r_{1}=\frac{-b-\sqrt{\Delta}}{2a}$
$r_{2}=\frac{-b+\sqrt{\Delta}}{2a}$

$\sqrt{\Delta}=\sqrt{1681}=41$
$r_{1}=\frac{-b-\sqrt{\Delta}}{2a}=\frac{-(-23)-41}{2*8}=\frac{-18}{16}
=-1+1/8
$
$r_{2}=\frac{-b+\sqrt{\Delta}}{2a}=\frac{-(-23)+41}{2*8}=\frac{64}{16}
=4
$