Derivative of x*sqrt(1+x^2)

1. Apply the product rule:

   $$\frac{d}{d x} f{\left(x \right)} g{\left(x \right)} = f{\left(x \right)} \frac{d}{d x} g{\left(x \right)} + g{\left(x \right)} \frac{d}{d x} f{\left(x \right)}$$

   $f{\left(x \right)} = x$; to find $\frac{d}{d x} f{\left(x \right)}$:

   1. Apply the power rule: $x$ goes to $1$

   $g{\left(x \right)} = \sqrt{x^{2} + 1}$; to find $\frac{d}{d x} g{\left(x \right)}$:

   1. Let $u = x^{2} + 1$.

   2. Apply the power rule: $\sqrt{u}$ goes to $\frac{1}{2 \sqrt{u}}$

   3. Then, apply the chain rule. Multiply by $\frac{d}{d x} \left(x^{2} + 1\right)$:

      1. Differentiate $x^{2} + 1$ term by term:

         1. The derivative of the constant $1$ is zero.

         2. Apply the power rule: $x^{2}$ goes to $2 x$

         The result is: $2 x$

      The result of the chain rule is:

      $$\frac{x}{\sqrt{x^{2} + 1}}$$

   The result is: $\frac{x^{2}}{\sqrt{x^{2} + 1}} + \sqrt{x^{2} + 1}$

2. Now simplify:

   $$\frac{2 x^{2} + 1}{\sqrt{x^{2} + 1}}$$

The answer is:

$$\frac{2 x^{2} + 1}{\sqrt{x^{2} + 1}}$$