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Bug in cos function in version 7.2

asked 2016-06-01 09:31:58 -0600

David E. Roberson gravatar image

updated 2016-06-02 05:00:43 -0600

slelievre gravatar image

I have 'SageMath version 7.2, Release Date: 2016-05-15' and when I enter cos(pi*(1+(5/63))) it returns cos(5/63*pi) which is incorrect (there should be a negative sign in front). Entering cos(N(pi)*(1+(5/63))) returns -0.969077286229078 which is correct, but entering N(cos(pi\*(1+(5/63)))) returns 0.969077286229078. Similar things happen when 5/63 is replaced with other fractions, but not always. Usually if the fraction is "nice", like 1/4 or 1/5 then it seems to get the right answer. I assume this has something to do with the exact answer being able to be expressed nicely with square roots, but I don't really know. Same happens with sin as far as I can tell. Anybody else having this problem?

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answered 2016-06-01 09:58:47 -0600

tmonteil gravatar image

updated 2016-06-01 10:05:32 -0600

This is clearly a bug, thanks for reporting ! This is now trac ticket 20752

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Asked: 2016-06-01 09:31:58 -0600

Seen: 107 times

Last updated: Jun 02 '16