Question 121
Inside a large circle three congruent small circles are constructed so that each small circle is tangent to the large circle and to the other two small circles. From an arbitrary point $M$, located on the large circle and different from the points of tangency, a tangent is drawn to each small circle. Let $l_{1}, l_{2}, l_{3}$ be the lengths of the tangent segments drawn from the point $M$ to the corresponding points of tangency on the small circles. Prove that one of these lengths is equal to the sum of the other two.