15k^2+70k-400=0

Solution for 15k^2+70k-400=0 equation:

15k^2+70k-400=0

a = 15; b = 70; c = -400;
Δ = b2-4ac
Δ = 702-4·15·(-400)
Δ = 28900
The delta value is higher than zero, so the equation has two solutions
We use following formulas to calculate our solutions:
$k_{1}=\frac{-b-\sqrt{\Delta}}{2a}$
$k_{2}=\frac{-b+\sqrt{\Delta}}{2a}$

$\sqrt{\Delta}=\sqrt{28900}=170$
$k_{1}=\frac{-b-\sqrt{\Delta}}{2a}=\frac{-(70)-170}{2*15}=\frac{-240}{30}
=-8
$
$k_{2}=\frac{-b+\sqrt{\Delta}}{2a}=\frac{-(70)+170}{2*15}=\frac{100}{30}
=3+1/3
$