Maths Olympiad Prep

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Number theory Difficulty 6.2 National olympiad Find the answer

How many ordered triples of positive integers (x,y,z)(x,y,z) satisfy (xy)z=64(x^y)^z=64?

Pick one

Solution

To solve the problem, we need to find all ordered triples (x,y,z)(x, y, z) of positive integers such that (xy)z=64(x^y)^z = 64. We start by expressing 64 as a power of a prime number:

64=26 64 = 2^6

This means we need to find all combinations of xx, yy, and zz such that:

(xy)z=26 (x^y)^z = 2^6

This can be rewritten as:

xyz=26 x^{yz} = 2^6

Since xx must be a power of 2 (because 64 is a power of 2), let x=2ax = 2^a where aa is a positive integer. Substituting x=2ax = 2^a into the equation, we get:

(2a)yz=26 (2^a)^{yz} = 2^6

This simplifies to:

2ayz=26 2^{ayz} = 2^6

Therefore, we must have:

ayz=6 ayz = 6

Now, we need to find all positive integer solutions (a,y,z)(a, y, z) such that ayz=6ayz = 6. We will consider each possible value of aa and find the corresponding pairs (y,z)(y, z).

1. **For a=1a = 1:**
yz=6 yz = 6
The possible pairs (y,z)(y, z) are:
(1,6),(2,3),(3,2),(6,1) (1, 6), (2, 3), (3, 2), (6, 1)
This gives us 4 solutions.

2. **For a=2a = 2:**
yz=3 yz = 3
The possible pairs (y,z)(y, z) are:
(1,3),(3,1) (1, 3), (3, 1)
This gives us 2 solutions.

3. **For a=3a = 3:**
yz=2 yz = 2
The possible pairs (y,z)(y, z) are:
(1,2),(2,1) (1, 2), (2, 1)
This gives us 2 solutions.

4. **For a=6a = 6:**
yz=1 yz = 1
The possible pair (y,z)(y, z) is:
(1,1) (1, 1)
This gives us 1 solution.

Summarizing all the solutions, we have:

4+2+2+1=9 4 + 2 + 2 + 1 = 9

Thus, the total number of ordered triples (x,y,z)(x, y, z) that satisfy the equation (xy)z=64(x^y)^z = 64 is:

9\boxed{9}

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Source: NuminaMath-1.5, licensed Apache-2.0. Statement and solution reproduced as published; topic and difficulty added by this site.