<s>[INST] Simplify $\frac{d}{dx}\frac{x^2}{1+\sqrt{x^2+1}}$ Simplify $$\frac{d}{dx}\frac{x^2}{1+\sqrt{x^2+1}}$$
I have manage to arrive to $$\frac{x^3+2x+2x\sqrt{x^2+1}}{(x^2+2)\sqrt{x^2+1}+2x^2+2}$$
But Wolfram manage to simplify to $$\frac{x}{\sqrt{x^2+1}}$$
 [/INST] Hint: Expand the fraction with $1-\sqrt{x^2+1}$:
$$\frac{x^2}{1+\sqrt{x^2+1}}  =\frac{x^2(1-\sqrt{x^2+1})}{1-(x^2+1)} = \sqrt{x^2+1}-1$$
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