6.7 An Application to Cyclic and BCH Codes

1.
a. If n = 1 it is clear, if n = 2, img. In general, img
c. If f = a0+ a1x + img then f′ = a1 + a3x2 + a5x4 + img = g(x2) where g = a1+ a3x + img. Conversely, f = g(x2) = b0+ b1x2 + b2x4 + img clearly implies that f′ = 0 (as 2 = 0 in img
3. If n = 2k then

img

and, by induction, img; that is 1 − xn = (1 + x)n. So the divisors of 1 − xn are 1, (1 + x), (1 + x)2, . . ., (1 + x)n, and these are a chain under divisibility.
Conversely, if 1− xn = (1 + x)kpm img where p is irreducible ...

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