Wrong simplification in symbolic trigonometry involving fractions

[tmonteil]

As reported in ​this ask question, Sage makes wrong simplifications in symbolic trigonometry involving fractions:

sage: cos(pi+pi*1/42)
cos(1/42*pi)

While it should be -cos(1/42*pi).

[rws]

Same with sin(pi+pi/42).

[tmonteil]

I do not have intermediate versions of Sage with me, but i confirm that it is a regression since on Sage 5.12, we have:

sage: cos(pi+pi*1/42)
cos(43/42*pi)
sage: sin(pi+pi/42)
sin(43/42*pi)

[rws]

No, the changes were just a few months ago, will get to it tomorrow.

[tmonteil]

More precisely, on a 7.2.beta4 version of Sage which i can reach by ssh, it works well:

sage: cos(pi+pi*1/42)
cos(43/42*pi)
sage: sin(pi+pi*1/42)
sin(43/42*pi)

So the regression is very recent, could it be due to the last update of pynac/ginac ?

[kcrisman]

So the regression is very recent, could it be due to the last update of pynac/ginac ?

Almost certainly so. See e.g. ​this bug, though I assume it is a different particular one.

[rws]

This is fixed and doctested in #20742.

[embray]

Determined to be invalid/duplicate/wontfix (closing as "wontfix" as a catch-all resolution).