MathDB
China Team Selection Test 2014 TST 1 Day 1 Q2

Source: China Nanjing , 12 Mar 2014

March 12, 2014
logarithmsanalytic geometrygraphing linesslopecombinatorics proposedcombinatoricsChina TST

Problem Statement

Let AA be a finite set of positive numbers , B={a+bc+d∣a,b,c,d∈A}B=\{\frac{a+b}{c+d} |a,b,c,d \in A \}. Show that: ∣B∣≥2∣A∣2−1\left | B \right | \ge 2\left | A \right |^2-1 , where ∣X∣|X| be the number of elements of the finite set XX. (High School Affiliated to Nanjing Normal University )
Back to ProblemsView on AoPS