# Correctness of Cosine doesnt work

**URL:** <https://cl.desmos.com/t/correctness-of-cosine-doesnt-work/7770>\
**Category:** Questions\
**Created:** [February 26, 2025, 1:42am UTC](https://cl.desmos.com/t/correctness-of-cosine-doesnt-work/7770 "2025-02-26T01:42:31Z")\
**Posts on this page:** 1\
**Page:** 1

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**Author:** ![AVIV\_ARDHILLAH\_RISQA](https://yyz1.discourse-cdn.com/flex031/user_avatar/cl.desmos.com/aviv_ardhillah_risqa/32/6490_2.png) [@AVIV\_ARDHILLAH\_RISQA](https://cl.desmos.com/u/AVIV_ARDHILLAH_RISQA)\
**Post date:** [February 26, 2025, 1:42am UTC](https://cl.desmos.com/t/correctness-of-cosine-doesnt-work/7770/1 "2025-02-26T01:42:31Z")

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this is the link of my activity  
[https://teacher.desmos.com/activitybuilder/custom/67b1241df2f43a53bdfcd175](https://teacher.desmos.com/activitybuilder/custom/67b1241df2f43a53bdfcd175)

this correctness work for most value of the number, but not for number 1.57… that is quarter arc. why this happen? can you give me solution?