To find all triples (x,y,z) of positive integers such that x≤y≤z and
x3(y3+z3)=2012(xyz+2),
we proceed as follows:
First, note that 2012⋅2=23⋅503. Taking the equation modulo x, we see that x∣2012. Therefore, x can be 1,2,4,503,1006,2012. We will consider the feasible values of x under the constraint x≤y≤z.
### Case 1: x=1
The equation becomes:
y3+z3=2012(yz+2).
Factoring the left-hand side, we get:
(y+z)(y2−yz+z2)=2012(yz+2).
For 503∣y+z or 503∣y2−yz+z2, we apply the lemma that 503∤y2−yz+z2 for positive integers y and z not both divisible by 503. Therefore, 503∣y+z. Let y+z=503n.
Rewriting the equation:
n(y2−yz+z2)=4(yz+2).
If n≥4, then (z−y)2≤2, implying z=y or z=y+1. Both cases lead to contradictions. Thus, n<4.
Since y and z have the same parity, n=2 is required, leading to y+z=1006. This results in:
(y+z)2=10062=5yz+4,
which is a contradiction modulo 5. Hence, no solutions exist for x=1.
### Case 2: x=2
The equation becomes:
y3+z3=503(yz+1).
Letting y+z=503n, we rewrite this as:
n(y2−yz+z2)=yz+1.
If n≥3, then n(z−y)2=1+(1−n)yz<0, a contradiction.
For n=1, we have:
y2−yz+z2=yz+1,
or (z−y)2=1, leading to z=y+1. Given y+z=503, we find y=251 and z=252. Verifying, (x,y,z)=(2,251,252) satisfies the original equation.
For n=2, we get:
2(y2−yz+z2)=yz+1,
or 2(z−y)2=1−yz, forcing y=z=1, which contradicts y+z=1006.
Thus, the only solution is (x,y,z)=(2,251,252).
The answer is: (2,251,252).