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发帖数: 243 | 1 A1. S is the set of all (h, k) with h, k non-negative integers such that h +
k < n. Each element of S is colored red or blue, so that if (h, k) is red and
h' <= h, k' <= k, then (h', k') is also red. A type 1 subset of S has n blue
elements with different first member and a type 2 subset of S has n blue
elements with different second member. Show that there are the same number of
type 1 and type 2 subsets.
A2. BC is a diameter of a circle center O. A is any point on the circle with
angle AOC > |
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