Mark M. answered 02/12/16
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Retired math prof. Calc 1, 2 and AP Calculus tutoring experience.
The formula is a3 - b3 = (a-b)(a2+ab+b2)
x6 - 64 = (x2)3 - (4)3
Substitute into the formula using a = x2 and b = 4
So, x6 - 64 = (x2-4)((x2)2+(x2)(4)+(4)2)
= (x-2)(x+2)(x4+4x2+16)