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B.Stat & B.Math 2022 - Q6

Source: Indian Statistical Institute (ISI) - B.Stat & B.Math Entrance 2022

May 8, 2022
isiIndian Statistical Institute2022Sequencelimitreal analysis

Problem Statement

Consider a sequence P1,P2,P_{1}, P_{2}, \ldots of points in the plane such that P1,P2,P3P_{1}, P_{2}, P_{3} are non-collinear and for every n4,Pnn \geq 4, P_{n} is the midpoint of the line segment joining Pn2P_{n-2} and Pn3P_{n-3}. Let LL denote the line segment joining P1P_{1} and P5P_{5}. Prove the following:
[*] The area of the triangle formed by the points Pn,Pn1,Pn2P_{n}, P_{n-1}, P_{n-2} converges to zero as nn goes to infinity.
[*] The point P9P_{9} lies on LL.