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Thread: Prove that cos is a rational number

  1. May 5th 2011, 11:31 PM #1
    andtom
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    Prove that cos is a rational number

    tan^{2} \alpha \in\mathbb{Q}

    Prove that

    cos^{2} \alpha \in\mathbb{Q} too.

    Thanks in advance!
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  2. May 6th 2011, 12:22 AM #2
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