105=4c^2

Solution for 105=4c^2 equation:

105=4c^2

We move all terms to the left:

105-(4c^2)=0

a = -4; b = 0; c = +105;
Δ = b2-4ac
Δ = 02-4·(-4)·105
Δ = 1680
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:

$\sqrt{\Delta}=\sqrt{1680}=\sqrt{16*105}=\sqrt{16}*\sqrt{105}=4\sqrt{105}$
$c_{1}=\frac{-b-\sqrt{\Delta}}{2a}=\frac{-(0)-4\sqrt{105}}{2*-4}=\frac{0-4\sqrt{105}}{-8}
=-\frac{4\sqrt{105}}{-8}
=-\frac{\sqrt{105}}{-2}
$
$c_{2}=\frac{-b+\sqrt{\Delta}}{2a}=\frac{-(0)+4\sqrt{105}}{2*-4}=\frac{0+4\sqrt{105}}{-8}
=\frac{4\sqrt{105}}{-8}
=\frac{\sqrt{105}}{-2}
$