-4k^2+64k+36=0

Solution for -4k^2+64k+36=0 equation:

-4k^2+64k+36=0

a = -4; b = 64; c = +36;
Δ = b2-4ac
Δ = 642-4·(-4)·36
Δ = 4672
The delta value is higher than zero, so the equation has two solutions
We use following formulas to calculate our solutions:
$k_{1}=\frac{-b-\sqrt{\Delta}}{2a}$
$k_{2}=\frac{-b+\sqrt{\Delta}}{2a}$

The end solution:

$\sqrt{\Delta}=\sqrt{4672}=\sqrt{64*73}=\sqrt{64}*\sqrt{73}=8\sqrt{73}$
$k_{1}=\frac{-b-\sqrt{\Delta}}{2a}=\frac{-(64)-8\sqrt{73}}{2*-4}=\frac{-64-8\sqrt{73}}{-8}
$
$k_{2}=\frac{-b+\sqrt{\Delta}}{2a}=\frac{-(64)+8\sqrt{73}}{2*-4}=\frac{-64+8\sqrt{73}}{-8}
$