Primitive Root of Unity

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Homework Statement


In F17, 2 is a primitive 8th root of unity. Evaluate f(x) = 7x3+8x2+3x+5 at the eight powers of 2 in F17. Verify that the method requires at most 16 multiplications in F17.


Homework Equations


You can can more clearly see the theorem on page 376-378 and the problem is on page 382 #6:
http://igortitara.files.wordpress.com/2010/04/a-concrete-introduction-to-higher-algebra1.pdf


The Attempt at a Solution


I was able to find that the d=3, but am unclear on how I evaluate f(x) based of Theorem 3.
 
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Answers and Replies

  • #2
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Homework Statement


In F17, 2 is a primitive 8th root of unity. Evaluate f(x) = 7x3+8x2+3x+5 at the eight powers of 2 in F17. Verify that the method requires at most 16 multiplications in F17.


Homework Equations


You can can more clearly see the theorem on page 376-378 and the problem is on page 382 #6:
http://igortitara.files.wordpress.com/2010/04/a-concrete-introduction-to-higher-algebra1.pdf


The Attempt at a Solution


I was able to find that the d=3, but am unclear on how I evaluate f(x) based of Theorem 3.

The question states that ##2## is a primitive ##2^3##'th root of unity, that is ##2^8 = e = 1##.

You need to evaluate ##f(2), f(2^2), f(2^3), ... , f(2^8)##. This requires at most ##2^r(r-1)## multiplications, which works out to:

##2^r(r-1) = 2^3(3-1) = 8(2) = 16##
 
Last edited:

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