3c^2-4c-25=0

Solution for 3c^2-4c-25=0 equation:

3c^2-4c-25=0

a = 3; b = -4; c = -25;
Δ = b2-4ac
Δ = -42-4·3·(-25)
Δ = 316
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:

$\sqrt{\Delta}=\sqrt{316}=\sqrt{4*79}=\sqrt{4}*\sqrt{79}=2\sqrt{79}$
$c_{1}=\frac{-b-\sqrt{\Delta}}{2a}=\frac{-(-4)-2\sqrt{79}}{2*3}=\frac{4-2\sqrt{79}}{6}
$
$c_{2}=\frac{-b+\sqrt{\Delta}}{2a}=\frac{-(-4)+2\sqrt{79}}{2*3}=\frac{4+2\sqrt{79}}{6}
$