1995 AIME Problem 2

Attempt Problem 2 of the 1995 AIME below, then check your answer against the professionally curated solution from LIVE by Po-Shen Loh. You can also try the full timed exam, view all 1995 AIME solutions, or check the answer key.

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2.

Find the last three digits of the product of the positive roots of 1995xlog1995x=x2.\sqrt{1995}\,x^{\log_{1995}x}=x^2.

Answer: 25
Concepts:logarithmquadraticmodular arithmetic
Difficulty rating: 1780
Small Hint:

Set y=log1995x,y=\log_{1995}x, so x=1995yx=1995^y

Big Hint:

Compare exponents of 19951995, then use the sum of the two values of yy

Solution:

Put y=log1995x,y=\log_{1995}x, so x=1995y.x=1995^y. The equation becomes 199512+y2=19952y,1995^{\frac{1}{2}+y^2}=1995^{2y}, and hence (y1)2=12.(y-1)^2=\frac{1}{2}. The two values of yy have sum 2,2, so the product of the corresponding positive roots is 19952.1995^2. Since 19955(mod1000),1995\equiv-5\pmod {1000}, its last three digits are 025.025. The requested AIME answer is 25.25.

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