Evaluate : `int x^(3) " cos " x^(4) " dx "`

Explanation

To evaluate the integral \( \int x^3 \cos(x^4) \, dx \), we can follow these steps:

### Step 1: Set up the integral
Let \( I = \int x^3 \cos(x^4) \, dx \).

### Step 2: Use substitution
We will use the substitution \( t = x^4 \). Then, we differentiate both sides to find \( dt \):
\[
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