
Pairwise Products
Problem
For any set of real numbers, R = {x, y, z}, let sum of pairwise products,
S = xy + xz + yz.
Given that x + y + z = 1, prove that S
1/3.
Problem ID: 224 (24 May 2005) Difficulty: 4 Star

For any set of real numbers, R = {x, y, z}, let sum of pairwise products,
S = xy + xz + yz.
Given that x + y + z = 1, prove that S
1/3.