To factor x4 - x ,
First use the form : ab + ac = a(b + c),
noting that here, "a" is "x", "b" is "x3", and "c" is "1" , to get:
x4 - x = x(x3 - 1).

The second factor above is a difference of two cubes, and factoring again, we get:
x4 - x = x(x - 1)(x2 + x + 1)

No more factoring is possible.

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