12r^2-11r-15=0

Solution for 12r^2-11r-15=0 equation:

12r^2-11r-15=0

a = 12; b = -11; c = -15;
Δ = b2-4ac
Δ = -112-4·12·(-15)
Δ = 841
The delta value is higher than zero, so the equation has two solutions
We use following formulas to calculate our solutions:
$r_{1}=\frac{-b-\sqrt{\Delta}}{2a}$
$r_{2}=\frac{-b+\sqrt{\Delta}}{2a}$

$\sqrt{\Delta}=\sqrt{841}=29$
$r_{1}=\frac{-b-\sqrt{\Delta}}{2a}=\frac{-(-11)-29}{2*12}=\frac{-18}{24}
=-3/4
$
$r_{2}=\frac{-b+\sqrt{\Delta}}{2a}=\frac{-(-11)+29}{2*12}=\frac{40}{24}
=1+2/3
$