Prove that the sum of three vectors determined by the medians of a triangle directed from the vertices is zero.

Explanation

To prove that the sum of the three vectors determined by the medians of a triangle directed from the vertices is zero, we can follow these steps:

### Step 1: Define the Triangle and Medians
Let triangle ABC have vertices A, B, and C. The midpoints of the sides BC, CA, and AB are denoted as D, E, and F, respectively. The medians AD, BE, and CF are drawn from vertices A, B, and C to the midpoints D, E, and F.

### Step 2: Express the Medians as Vectors
The vectors representing the medians can be expressed as:
- **Median AD**:
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