Applicare la formula: $\frac{a}{\frac{b}{c}}$$=\frac{ac}{b}$, dove $a=1$, $b=\sqrt{1+x^2}$, $c=x$, $a/b/c=\frac{1}{\frac{\sqrt{1+x^2}}{x}}$ e $b/c=\frac{\sqrt{1+x^2}}{x}$

Applicare la formula: $b\cdot dy=a\cdot dx$$\to \int bdy=\int adx$, dove $a=\frac{x}{\sqrt{1+x^2}}$, $b=\frac{1}{\sqrt{1+y^2}}$, $dyb=dxa=\frac{1}{\sqrt{1+y^2}}dy=\frac{x}{\sqrt{1+x^2}}dx$, $dyb=\frac{1}{\sqrt{1+y^2}}dy$ e $dxa=\frac{x}{\sqrt{1+x^2}}dx$