x*x+15=800

Solution for x*x+15=800 equation:

x*x+15=800

We move all terms to the left:

x*x+15-(800)=0

We add all the numbers together, and all the variables

x*x-785=0

Wy multiply elements

x^2-785=0

a = 1; b = 0; c = -785;
Δ = b2-4ac
Δ = 02-4·1·(-785)
Δ = 3140
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:

$\sqrt{\Delta}=\sqrt{3140}=\sqrt{4*785}=\sqrt{4}*\sqrt{785}=2\sqrt{785}$
$x_{1}=\frac{-b-\sqrt{\Delta}}{2a}=\frac{-(0)-2\sqrt{785}}{2*1}=\frac{0-2\sqrt{785}}{2}
=-\frac{2\sqrt{785}}{2}
=-\sqrt{785}
$
$x_{2}=\frac{-b+\sqrt{\Delta}}{2a}=\frac{-(0)+2\sqrt{785}}{2*1}=\frac{0+2\sqrt{785}}{2}
=\frac{2\sqrt{785}}{2}
=\sqrt{785}
$