5x^2-91=0

Solution for 5x^2-91=0 equation:

5x^2-91=0

a = 5; b = 0; c = -91;
Δ = b2-4ac
Δ = 02-4·5·(-91)
Δ = 1820
The delta value is higher than zero, so the equation has two solutions
We use following formulas to calculate our solutions:
$x_{1}=\frac{-b-\sqrt{\Delta}}{2a}$
$x_{2}=\frac{-b+\sqrt{\Delta}}{2a}$

The end solution:

$\sqrt{\Delta}=\sqrt{1820}=\sqrt{4*455}=\sqrt{4}*\sqrt{455}=2\sqrt{455}$
$x_{1}=\frac{-b-\sqrt{\Delta}}{2a}=\frac{-(0)-2\sqrt{455}}{2*5}=\frac{0-2\sqrt{455}}{10}
=-\frac{2\sqrt{455}}{10}
=-\frac{\sqrt{455}}{5}
$
$x_{2}=\frac{-b+\sqrt{\Delta}}{2a}=\frac{-(0)+2\sqrt{455}}{2*5}=\frac{0+2\sqrt{455}}{10}
=\frac{2\sqrt{455}}{10}
=\frac{\sqrt{455}}{5}
$