Question

Why does dS=\sqrt{1+(f_{x})^{2}+(f _{y})^{2}}dA ?

Answer 1

IF it requires to much explaining just hit me with a link. I was looking at Paul's Notes earlier (the website) but couldn't find an explanation

Answer 2

\[dS=\sqrt{1+(f_{x})^{2}+(f _{y})^{2}}dA\]