I have to answer the following and support it with a full proof.

Is cos(5°) rational? (Given hint: show that if cos(x) is rational, then cos(3x) is rational).

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- November 1st 2006, 06:50 PMharoldCosine Proof
I have to answer the following and support it with a full proof.

Is cos(5°) rational? (Given hint: show that if cos(x) is rational, then cos(3x) is rational). - November 1st 2006, 06:59 PMThePerfectHacker
- November 1st 2006, 07:46 PMharold
Hi THP,

I was thinking the exact same thing by showing cos(45°) but it still doesn't__prove__it since we need to show if cos x is rational, then cos 3x is rational....then show cos 5° is irrat. based on the previous two proofs...? - November 1st 2006, 07:53 PMThePerfectHacker