x2-81=9

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Solution for x2-81=9 equation:



x2-81=9
We move all terms to the left:
x2-81-(9)=0
We add all the numbers together, and all the variables
x^2-90=0
a = 1; b = 0; c = -90;
Δ = b2-4ac
Δ = 02-4·1·(-90)
Δ = 360
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:
$\sqrt{\Delta}=\sqrt{360}=\sqrt{36*10}=\sqrt{36}*\sqrt{10}=6\sqrt{10}$
$x_{1}=\frac{-b-\sqrt{\Delta}}{2a}=\frac{-(0)-6\sqrt{10}}{2*1}=\frac{0-6\sqrt{10}}{2} =-\frac{6\sqrt{10}}{2} =-3\sqrt{10} $
$x_{2}=\frac{-b+\sqrt{\Delta}}{2a}=\frac{-(0)+6\sqrt{10}}{2*1}=\frac{0+6\sqrt{10}}{2} =\frac{6\sqrt{10}}{2} =3\sqrt{10} $

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