Express cos(*t*) as a rational function of
cos^{3}(*t*) and sin^{3}(*t*), i.e. find
polynomials *P*(*x*,*y*) and *Q*(*x*,*y*)
such that cos(*t*) =
*P*(cos^{3}(*t*),sin^{3}(*t*)) /
*Q*(cos^{3}(*t*),sin^{3}(*t*)).

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Source: I. S. Cohen
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