**1-**Find all the three-digit numbers for which one obtains, when dividing the number by 11, the sum of the squares of the digits of the initial number.

**2-**For which real numbers x does the following inequality hold :

**3-**A right-angled triangle ABC is given for which the hypotenuse BC has length a and is divided into n equal segments, where n is odd. Let α be the angle with which the point A sees the segment containing themiddle of the hypotenuse.Prove that:

where h is the height of the triangle.