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1/(b-c)^2 +1/(c-a)^2 +1/(a-b)^2 is square of a rational for rational a,b,c

Source: 1976 Swedish Mathematical Competition p3

March 26, 2021
algebraPerfect Squarerational

Problem Statement

If aa, bb, cc are rational, show that 1(bc)2+1(ca)2+1(ab)2 \frac{1}{(b-c)^2}+\frac{1}{(c-a)^2}+\frac{1}{(a-b)^2} is the square of a rational.