# Question about Chebyshev Coefficients in CKKS Bootstrapping

**URL:** <https://openfhe.discourse.group/t/question-about-chebyshev-coefficients-in-ckks-bootstrapping/2125>\
**Category:** Library Questions\
**Created:** [August 5, 2025, 3:56pm UTC](https://openfhe.discourse.group/t/question-about-chebyshev-coefficients-in-ckks-bootstrapping/2125 "2025-08-05T15:56:08Z")\
**Posts on this page:** 1\
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**Author:** ![andreea.alexandru](https://yyz1.discourse-cdn.com/flex031/user_avatar/openfhe.discourse.group/andreea.alexandru/32/378_2.png) [@andreea.alexandru](https://openfhe.discourse.group/u/andreea.alexandru)\
**Post date:** [August 5, 2025, 4:32pm UTC](https://openfhe.discourse.group/t/question-about-chebyshev-coefficients-in-ckks-bootstrapping/2125/2 "2025-08-05T16:32:05Z")

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For precision reasons, we do not directly evaluate the sine function, but use several iterations of the double angle formula. Please see [this response](https://openfhe.discourse.group/t/approximate-modular-reduction-during-bootstrapping/2119) and the reference cited there.

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