prove
(a^2-b^2)^3+(b^2-c^2)^3+(c^2-a^2)^3=3(a^2-b^2)(b^2-c^2)(c^2-a^2)
The following replacement may not always work, but it works in this case, and simplifies the problem.
Try replacing a² by A, b² by B and c² by C in the given expression.
Expand the left-hand side:
(A-B)³ + (B-c)³ + (C-A)³
=A³-3A²B+3AB²-B³+
B³-3B²C+3BC²-C³+
C³-3C²A+3CA²-A³
=-3A²B+3AB²-3B²C+3BC²-3C²A+3CA²
=3(-A²B+AB²-B²C+BC²-C²A+CA²)
=3(A-B)(B-C)(C-A)
The last factorization is not obvious, but can be inspired by expanding the right-hand side.