Jose S. answered 06/06/14
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Whenever you have exponents that are multiples of each other consider using substitution as follows:
Let u = x^3, then u^2=x^6, and your expression becomes: u^2-u-6. The quadratic should be straightfoward to factor(though if you need help feel free to ask), and after you factor it you can substiute x back in.
Hope this helps.