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# INMO 2012 | Problems

1. This post contains problems from Indian National Mathematics Olympiad, INMO 2012. Try them and share your solution in the comments.
2.
3. Let ABCD be a quadrilateral inscribed in a circle. Suppose AB =$\sqrt {2 + \sqrt {2} }$ and AB subtends 1350 at the center of the circle. Find the maximum possible area of ABCD.
4. Let $p_1 and $q_1 be two sets of prime numbers such that $p_4 - p_1 = 8$  and $q_4 - q_1 = 8$ . Suppose $p_1>5$ and $q_1>5$ . Prove that 30 divides $p_1 - q_1$.
5. Define a sequence $$ n∈N of functions as $f_0(x )=1, f_1(x )=x$, $(f_n(x))^2 - 1 = f_{n-1} (x) f_{n+1} (x)$, for $n \ge 1$ . Prove that each $f_n(x )$ is a polynomial with integer coefficients.
6. Let ABC be a triangle. An interior point P of ABC is said to be good if we can find exactly 27 rays emanating from P intersecting the sides of the triangle ABC such that the triangle is divided by these rays into 27 smaller triangles of equal area. Determine the number of good points for a given triangle ABC.
7. Let ABC be an acute angled triangle. Let D, E, F be points on BC, CA, AB such that AD is the median, BE is the internal bisector and CF is the altitude. Suppose that angle FDE = angle C and angle DEF = angle A and angle EFD = angle B. Show that ABC is equilateral.
8. Let $f :Z \mapsto Z$be a function satisfying $f(0) \neq 0$ , $f(1)=0$ and
1. $f(xy) + f(x)f(y) = f(x) + f(y)$,
2. $(f(x-y) - f(0) ) f(x) f(y) = 0$ for all x , $y in Z$ simultaneously.
1. Find the set of all possible values of the function f.
2. If $f(10) \neq 0$ and $f(2) = 0$, find the set of all integers n such that $f(n) \neq 0$ .

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## By Dr. Ashani Dasgupta

Ph.D. in Mathematics, University of Wisconsin, Milwaukee, United States.

Research Interest: Geometric Group Theory, Relatively Hyperbolic Groups.

Founder, Cheenta

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