7c2=91

Solution for 7c2=91 equation:

7c^2=91

We move all terms to the left:

7c^2-(91)=0

a = 7; b = 0; c = -91;
Δ = b2-4ac
Δ = 02-4·7·(-91)
Δ = 2548
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:

$\sqrt{\Delta}=\sqrt{2548}=\sqrt{196*13}=\sqrt{196}*\sqrt{13}=14\sqrt{13}$
$c_{1}=\frac{-b-\sqrt{\Delta}}{2a}=\frac{-(0)-14\sqrt{13}}{2*7}=\frac{0-14\sqrt{13}}{14}
=-\frac{14\sqrt{13}}{14}
=-\sqrt{13}
$
$c_{2}=\frac{-b+\sqrt{\Delta}}{2a}=\frac{-(0)+14\sqrt{13}}{2*7}=\frac{0+14\sqrt{13}}{14}
=\frac{14\sqrt{13}}{14}
=\sqrt{13}
$