To find the derivative of the function \( f(x) = (x^2 + 1) e^{4x} \), we will use the product rule of differentiation. The product rule states that if you have a function \( f(x) = u(x) \cdot v(x) \), then the derivative \( f'(x) = u'(x) \cdot v(x) + u(x) \cdot v'(x) \). Here, \( u(x) = x^2 + 1 \) and \( v(x) = e^{4x} \). We will differentiate each part separately and then apply the product rule.
Step 1: Define the Function
We start with the function defined as:
\[
f(x) = (x^2 + 1) e^{4x}
\]
Step 2: Differentiate the Components
We identify the components of the function:
Let \( u = x^2 + 1 \)
Let \( v = e^{4x} \)
Next, we compute the derivatives of \( u \) and \( v \):
\[
u' = \frac{d}{dx}(x^2 + 1) = 2x
\]
\[
v' = \frac{d}{dx}(e^{4x}) = 4e^{4x}
\]
Step 3: Apply the Product Rule
Using the product rule, we find the derivative \( f'(x) \):
\[
f'(x) = u'v + uv' = (2x)e^{4x} + (x^2 + 1)(4e^{4x})
\]
Step 4: Simplify the Expression
We can factor out \( e^{4x} \) from the expression:
\[
f'(x) = e^{4x}(2x + 4(x^2 + 1)) = e^{4x}(2x + 4x^2 + 4)
\]
Final Answer
Thus, the derivative of the function is:
\[
\boxed{f'(x) = e^{4x}(4x^2 + 2x + 4)}
\]