A bar of given length moves with its extremities on two fixed straight lines at right angles. Show that any point on the bar describes an ellipse.

Explanation

To show that any point on a bar of given length, moving with its extremities on two fixed straight lines at right angles, describes an ellipse, we can follow these steps:

### Step-by-Step Solution:

1. **Define the Setup**:
- Let the two fixed lines be the x-axis (OX) and the y-axis (OY).
- Let the length of the bar be \( L \).
- Let the endpoints of the bar be \( A \) and \( B \).
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