once use the command below:
C-x RET C-\ TeX RET
I try to make some math formula:
but it can't be automatic translated to √,
then I check the symbol list:
and also can't find the \sqrt tex item,
so is there a config I have missed?
No, you're not missing anything. For whatever reason, the TeX input method doesn't include include the macro
\sqrt. You can get that symbol under its secret name,
This is arguably a bug which could be fixed by inserting a rule for
\sqrt in the
latin-ltx--define-rules form in the file
leim/quail/latin-ltx.el. I don't follow that macro, but it would probably also be possible to add the rule in your config if you knew the name of the appropriate variable (which I don't as of yet).
Bug report submitted to https://debbugs.gnu.org/cgi/bugreport.cgi?bug=25594 ...