Let n be an integer greater than 1 and let n√2∈R be the unique positive n-th root of 2. Show that the real numbers 1,(n√2)2,⋅⋅⋅,(n√2)n−1 are linearly independent over Q.
Using the definition of linear independence, the problem is equivalent to showing that
c1+c2(n√2)2+⋅⋅⋅+cn−1(n√2)n−1=0
has only the trivial solution c1=c2=⋅⋅⋅=cn−1=0
I believe there is something special about each n√2 being a unique positive n-th root of 2 that allows us to state linear independence. In particular, this implies that each (n√2)i is linearly independent where i∈{0,2,3,⋅⋅⋅,n−1}.
I don't know if my intuition is correct and how to prove this linear independence rigorously.
Answer
Hint: if there were a linear dependence relation between these elements, then n√2 would satisfy a (monic) polynomial of degree ⩽ (after dividing by the highest nonzero coefficient). On the other hand, \sqrt[n]{2} is a root of X^{n} - 2, which is irreducible over \mathbb{Q} by Eisenstein at 2. Why is this first bit in contradiction with the second fact?
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