[tex] \text{In loc de G voi folosi litera f.}\\ \displaystyle f'(x)=arctg\,'x = \frac{1}{1+x^2} = g(x) \\ \\
\Longrightarrow \int{g(x)}dx= \int{\frac{1}{1+x^2}}\,dx = arctg\,x = f(x)\\ \\
\Longrightarrow ~f(x) = arctg\,x ~este~primitiva~functiei~g(x) = \frac{1}{1+x^2}[/tex]