16+(x*x)=81

Solution for 16+(x*x)=81 equation:

16+(x*x)=81

We move all terms to the left:

16+(x*x)-(81)=0

We add all the numbers together, and all the variables

(+x*x)+16-81=0

We add all the numbers together, and all the variables

(+x*x)-65=0

We get rid of parentheses

x*x-65=0

Wy multiply elements

x^2-65=0

a = 1; b = 0; c = -65;
Δ = b2-4ac
Δ = 02-4·1·(-65)
Δ = 260
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:

$\sqrt{\Delta}=\sqrt{260}=\sqrt{4*65}=\sqrt{4}*\sqrt{65}=2\sqrt{65}$
$x_{1}=\frac{-b-\sqrt{\Delta}}{2a}=\frac{-(0)-2\sqrt{65}}{2*1}=\frac{0-2\sqrt{65}}{2}
=-\frac{2\sqrt{65}}{2}
=-\sqrt{65}
$
$x_{2}=\frac{-b+\sqrt{\Delta}}{2a}=\frac{-(0)+2\sqrt{65}}{2*1}=\frac{0+2\sqrt{65}}{2}
=\frac{2\sqrt{65}}{2}
=\sqrt{65}
$