Talk:Sum of arctan identity question/@comment-88.108.243.179-20140114233220

There appears to be a (trivial) sign error in your above text (doesn't affect tresult):

Above your line "So the left-hand-side of the identity to be proven is", the final term is (x*x - y*y)

But below that line you have (apparently incorrectly) substituted (x*x + y*y) as the final term.

With that plus replaced by a minus, your text and your logic reads flawlessly - thank you.

[You may also wish to remove the 'y' from 'replacying' in your penult line.]