Derivative of x*sin(3x^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 $1$

   $g{\left(x \right)} = \sin{\left(3 x^{2} \right)}$; to find $\frac{d}{d x} g{\left(x \right)}$:

   1. Let $u = 3 x^{2}$.

   2. The derivative of sine is cosine:

      $$\frac{d}{d u} \sin{\left(u \right)} = \cos{\left(u \right)}$$

   3. Then, apply the chain rule. Multiply by $\frac{d}{d x} 3 x^{2}$:

      1. The derivative of a constant times a function is the constant times the derivative of the function.

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

         So, the result is: $6 x$

      The result of the chain rule is:

      $$6 x \cos{\left(3 x^{2} \right)}$$

   The result is: $6 x^{2} \cos{\left(3 x^{2} \right)} + \sin{\left(3 x^{2} \right)}$

The answer is:

$$6 x^{2} \cos{\left(3 x^{2} \right)} + \sin{\left(3 x^{2} \right)}$$