9x^2-1=15+5

Solution for 9x^2-1=15+5 equation:

9x^2-1=15+5

We move all terms to the left:

9x^2-1-(15+5)=0

We add all the numbers together, and all the variables

9x^2-1-20=0

We add all the numbers together, and all the variables

9x^2-21=0

a = 9; b = 0; c = -21;
Δ = b2-4ac
Δ = 02-4·9·(-21)
Δ = 756
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:

$\sqrt{\Delta}=\sqrt{756}=\sqrt{36*21}=\sqrt{36}*\sqrt{21}=6\sqrt{21}$
$x_{1}=\frac{-b-\sqrt{\Delta}}{2a}=\frac{-(0)-6\sqrt{21}}{2*9}=\frac{0-6\sqrt{21}}{18}
=-\frac{6\sqrt{21}}{18}
=-\frac{\sqrt{21}}{3}
$
$x_{2}=\frac{-b+\sqrt{\Delta}}{2a}=\frac{-(0)+6\sqrt{21}}{2*9}=\frac{0+6\sqrt{21}}{18}
=\frac{6\sqrt{21}}{18}
=\frac{\sqrt{21}}{3}
$