4c^2-2c-15=0

Solution for 4c^2-2c-15=0 equation:

4c^2-2c-15=0

a = 4; b = -2; c = -15;
Δ = b2-4ac
Δ = -22-4·4·(-15)
Δ = 244
The delta value is higher than zero, so the equation has two solutions
We use following formulas to calculate our solutions:
$c_{1}=\frac{-b-\sqrt{\Delta}}{2a}$
$c_{2}=\frac{-b+\sqrt{\Delta}}{2a}$

The end solution:

$\sqrt{\Delta}=\sqrt{244}=\sqrt{4*61}=\sqrt{4}*\sqrt{61}=2\sqrt{61}$
$c_{1}=\frac{-b-\sqrt{\Delta}}{2a}=\frac{-(-2)-2\sqrt{61}}{2*4}=\frac{2-2\sqrt{61}}{8}
$
$c_{2}=\frac{-b+\sqrt{\Delta}}{2a}=\frac{-(-2)+2\sqrt{61}}{2*4}=\frac{2+2\sqrt{61}}{8}
$