15k^2-26k-21=0

Solution for 15k^2-26k-21=0 equation:

15k^2-26k-21=0

a = 15; b = -26; c = -21;
Δ = b2-4ac
Δ = -262-4·15·(-21)
Δ = 1936
The delta value is higher than zero, so the equation has two solutions
We use following formulas to calculate our solutions:
$k_{1}=\frac{-b-\sqrt{\Delta}}{2a}$
$k_{2}=\frac{-b+\sqrt{\Delta}}{2a}$

$\sqrt{\Delta}=\sqrt{1936}=44$
$k_{1}=\frac{-b-\sqrt{\Delta}}{2a}=\frac{-(-26)-44}{2*15}=\frac{-18}{30}
=-3/5
$
$k_{2}=\frac{-b+\sqrt{\Delta}}{2a}=\frac{-(-26)+44}{2*15}=\frac{70}{30}
=2+1/3
$