Derivative of y=x(2x+1)³

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 $1$

   $g{\left(x \right)} = \left(2 x + 1\right)^{3}$; to find $\frac{d}{d x} g{\left(x \right)}$:

   1. Let $u = 2 x + 1$.

   2. Apply the power rule: $u^{3}$ goes to $3 u^{2}$

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

      1. Differentiate $2 x + 1$ term by term:

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

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

            So, the result is: $2$

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

         The result is: $2$

      The result of the chain rule is:

      $$6 \left(2 x + 1\right)^{2}$$

   The result is: $6 x \left(2 x + 1\right)^{2} + \left(2 x + 1\right)^{3}$

2. Now simplify:

   $$\left(2 x + 1\right)^{2} \left(8 x + 1\right)$$

The answer is:

$$\left(2 x + 1\right)^{2} \left(8 x + 1\right)$$