Evaluate `sum_(r=1)^(n)rxxr!`

Explanation

To evaluate the summation \( \sum_{r=1}^{n} r \cdot r! \), we can follow these steps:

### Step 1: Rewrite the term \( r \cdot r! \)
We know that \( r \cdot r! = r! \cdot r = (r + 1 - 1) \cdot r! = (r + 1)! - r! \). This allows us to express the term in a more manageable form.

### Step 2: Substitute into the summation
Now, we can substitute this expression back into the summation:
\[
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