fix cot.as_real_imag

[gschintgen]

References to other Issues or PRs

Fixes #19366

Brief description of what is fixed or changed

Sign error in the formula.

Other comments

The patch has kindly been provided by the reporter. (See #19366 for a proof of its validity.)

Release Notes

• functions
  • Fixed cot.as_real_imag (sign error in imaginary part)

[sympy-bot]

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• functions
  • Fixed cot.as_real_imag (sign error in imaginary part) (#19468 by @DaveWitteMorris and @gschintgen)

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#### References to other Issues or PRs
Fixes #19366 

#### Brief description of what is fixed or changed
Sign error in the formula.

#### Other comments
The patch has kindly been provided by the reporter. (See #19366 for a proof of its validity.)

#### Release Notes

<!-- Write the release notes for this release below. See
https://github.com/sympy/sympy/wiki/Writing-Release-Notes for more information
on how to write release notes. The bot will check your release notes
automatically to see if they are formatted correctly. -->

<!-- BEGIN RELEASE NOTES -->
* functions
  * Fixed `cot.as_real_imag` (sign error in imaginary part)
<!-- END RELEASE NOTES -->

Update

The release notes on the wiki have been updated.

[codecov]

Codecov Report

Merging #19468 into master will increase coverage by 0.019%.
The diff coverage is 100.000%.

@@              Coverage Diff              @@
##            master    #19468       +/-   ##
=============================================
+ Coverage   75.638%   75.658%   +0.019%     
=============================================
  Files          652       652               
  Lines       169756    169756               
  Branches     40072     40072               
=============================================
+ Hits        128401    128434       +33     
+ Misses       35742     35711       -31     
+ Partials      5613      5611        -2     

[oscarbenjamin]

Looks good. Thanks!