7x^2-1=4

Solution for 7x^2-1=4 equation:

7x^2-1=4

We move all terms to the left:

7x^2-1-(4)=0

We add all the numbers together, and all the variables

7x^2-5=0

a = 7; b = 0; c = -5;
Δ = b2-4ac
Δ = 02-4·7·(-5)
Δ = 140
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:

$\sqrt{\Delta}=\sqrt{140}=\sqrt{4*35}=\sqrt{4}*\sqrt{35}=2\sqrt{35}$
$x_{1}=\frac{-b-\sqrt{\Delta}}{2a}=\frac{-(0)-2\sqrt{35}}{2*7}=\frac{0-2\sqrt{35}}{14}
=-\frac{2\sqrt{35}}{14}
=-\frac{\sqrt{35}}{7}
$
$x_{2}=\frac{-b+\sqrt{\Delta}}{2a}=\frac{-(0)+2\sqrt{35}}{2*7}=\frac{0+2\sqrt{35}}{14}
=\frac{2\sqrt{35}}{14}
=\frac{\sqrt{35}}{7}
$