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

Prove that

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

Thanks in advance!

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- May 5th 2011, 11:31 PMandtomProve that cos is a rational number
$\displaystyle tan^{2} \alpha \in\mathbb{Q} $

Prove that

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

Thanks in advance! - May 6th 2011, 12:22 AMProve It