Pregunta: 18. f(x,y)=x2+y2−251

Given that,

$\mathrm{f}(\mathrm{x},\mathrm{y})=\frac{1}{\sqrt{{\mathrm{x}}^2+{\mathrm{y}}^2-25}}$

Set the radicand in $\sqrt{{\mathrm{x}}^2+{\mathrm{y}}^2-25}$ greater than or equal to $0$ to find where the expression is defined.