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crappyjones
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field extension question (abstract algebra)
For any positive integers a, b, show that Q(sqrt a + sqrt b) = Q(sqrt a, sqrt b).
i proved that [Q(sqrt a):Q] for all n belonging to Z+ is 2 whenever a is not a perfect square and 1 when it is. also, for Q(sqrt a, sqrt b) i found the minimal polynomial to be (x2-a-b)2 - 4ab. for Q(sqrt a + sqrt b), i found the minimal polynomial to be x4 - 2ax2 - 2bx2 + a2 + b2 - 2ab.
i can show that both extensions have degree 4 (for both a and b non perfect squares, 3 for when either a or b is a perfect square, 2 for when both a and b are perfect squares) and that the basis of Q(sqrt a, sqrt b) is {1, sqrt a, sqrt b, sqrt (ab)}.
any thoughts on how to solve this problem? am i on the right track? completely off? any comments on what i am doing would be appreciated as well.
thanks,
cj.
Homework Statement
For any positive integers a, b, show that Q(sqrt a + sqrt b) = Q(sqrt a, sqrt b).
Homework Equations
The Attempt at a Solution
i proved that [Q(sqrt a):Q] for all n belonging to Z+ is 2 whenever a is not a perfect square and 1 when it is. also, for Q(sqrt a, sqrt b) i found the minimal polynomial to be (x2-a-b)2 - 4ab. for Q(sqrt a + sqrt b), i found the minimal polynomial to be x4 - 2ax2 - 2bx2 + a2 + b2 - 2ab.
i can show that both extensions have degree 4 (for both a and b non perfect squares, 3 for when either a or b is a perfect square, 2 for when both a and b are perfect squares) and that the basis of Q(sqrt a, sqrt b) is {1, sqrt a, sqrt b, sqrt (ab)}.
any thoughts on how to solve this problem? am i on the right track? completely off? any comments on what i am doing would be appreciated as well.
thanks,
cj.
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