25=16+x*x

Solution for 25=16+x*x equation:

25=16+x*x

We move all terms to the left:

25-(16+x*x)=0

We add all the numbers together, and all the variables

-(x*x+16)+25=0

We get rid of parentheses

-x*x-16+25=0

We add all the numbers together, and all the variables

-x*x+9=0

Wy multiply elements

-1x^2+9=0

a = -1; b = 0; c = +9;
Δ = b2-4ac
Δ = 02-4·(-1)·9
Δ = 36
The delta value is higher than zero, so the equation has two solutions
We use following formulas to calculate our solutions:
$x_{1}=\frac{-b-\sqrt{\Delta}}{2a}$
$x_{2}=\frac{-b+\sqrt{\Delta}}{2a}$

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