Write the number of diagonals of an n-sided polygon.

Explanation

To find the number of diagonals in an n-sided polygon, we can follow these steps:

### Step-by-Step Solution:

1. **Understand the Polygon**: An n-sided polygon has n vertices. Each vertex can connect to other vertices to form diagonals.

2. **Choosing Vertices**: To form a diagonal, we need to choose 2 vertices from the n vertices. The number of ways to choose 2 vertices from n is given by the combination formula:
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