Toán học, Olympic toán toàn quốc - Việt nam 2002

A1. Solve the following equation: �"(4 - 3�"(10 - 3x)) = x - 2.

A2. ABC is an isosceles triangle with AB = AC. O is a variable point on the line BC such that the circle center O radius OA does not have the lines AB or AC as tangents. The lines AB, AC meet the circle again at M, N respectively. Find the locus of the orthocenter of the triangle AMN.

A3. m < 2001 and n < 2002 are fixed positive integers. A set of distinct real numbers are arranged in an array with 2001 rows and 2002 columns. A number in the array is bad if it is smaller than at least m numbers in the same column and at least n numbers in the same row. What is the smallest possible number of bad numbers in the array?

B1. If all the roots of the polynomial x3 + a x2 + bx + c are real, show that 12ab + 27c d" 6a3 + 10(a2 - 2b)3/2. When does equality hold?

B2. Find all positive integers n for which the equation a + b + c + d = n�"(abcd) has a solution in positive integers.

B3. n is a positive integer. Show that the equation 1/(x - 1) + 1/(22x - 1) + ... + 1/(n2x - 1) = 1/2 has a unique solution xn > 1. Show that as n tends to infinity, xn tends to 4.