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In: Advanced Math

An element a in a field F is called a primitive nth root of unity if...

An element a in a field F is called a primitive nth root of unity if n is the smallest positive integer such that an=1. For example, i is a primitive 4th root of unity in C, whereas -1 is not a primitive 4th root of unity (even though (-1)4=1).

(a) Find all primitive 4th roots of unity in F5

(b) Find all primitive 3rd roots of unity in F7

(c) Find all primitive 6th roots of unity in F7

(d) Use Lagrange's Theorem to prove that if n does not divide p-1, then Fp contains no nth roots of unity. [In fact, the converse is true: If n divides p-1, then Fp contains a (primitive) pth root of unity. We will prove this later.]

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