As we now the square root of (-3)^2+(-4)^2 is the square root of 25 equal to 5. However we got a strange error calling xfp package and Tikz saying:
\LaTeX3 error: Invalid operation sqrt(-25) Below is the code:
\documentclass{standalone}
\usepackage{tikz}
\usepackage{xfp}
\begin{document}
\begin{tikzpicture}
\edef\u{-3};
\edef\v{-4};
\edef\w{\fpeval{sqrt(\fpeval{\u^2}+\fpeval{\v^2})}};
\node at (0,0) {Ans=\fpeval{\w}};
\end{tikzpicture}
\end{document}