Is there an identity for the cos( 1/3 x ) ?

  • Thread starter swampwiz
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  • #1
swampwiz
486
44
It seems that this term comes up in solving the cubic equation. While there is the identity for the half-angle, there doesn't seem to be one for third-angle.
 

Answers and Replies

  • #3
JJacquelin
801
34
Hi !

The identity involves complex terms :
 

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  • #4
swampwiz
486
44
OK, I understand the general form. I didn't think to use an integer fraction in lieu of an integer. (Actually, it appears that *any* number could be used there.)
 

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