Salut,
[tex]\left(\dfrac{f}g\right)^{'}=\dfrac{f^{'}\cdot g-f\cdot g^{'}}{g^2}\\\\\left(\dfrac{2x}{\sqrt{x^2+4}}\right)^{'}=\dfrac{(2x)^{'}\cdot \sqrt{x^2+4}-2x\cdot (\sqrt{x^2+4})^{'}}{(\sqrt{x^2+4})^2}=\dfrac{2\cdot \sqrt{x^2+4}-2x\cdot\dfrac{2x}{2\sqrt{x^2+4}}}{x^2+4}=\\\\=\dfrac{2(x^2+4)-2x^2}{(x^2+4)\sqrt{x^2+4}}=\dfrac{8}{(x^2+4)\sqrt{x^2+4}}.[/tex]
Green eyes.
