extrude
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If you mean you want to not see the edges on the back side, is not blocking them also going to block the grids that appear to be inside your Solid?
Read up in Help about the HIDE and SHADE commands and the SHADEMODE System Variable.
Kent Cooper, AIA 
Hi and Welcome to AutoDesk Forum,
>> why everytime i am using extrude this line will appear << this happened if:
- the Extrusion mode not solid
Command: EXTRUDE
Current wire frame density: ISOLINES=4, Closed profiles creation mode = Surface
Select objects to extrude or [MOde]: *Cancel*
- the Polyline not closed.
- your object not polyline,just joined lines.
Imad Habash
@Kent1Cooper wrote:
....
If you mean you want to not see the edges on the back side, is not blocking them also going to block the grids that appear to be inside your Solid?
....
If it seems like I didn't understand [you were talking about those grids], it's because of an oddity I just discovered. When I first double-clicked on your attachment, it opened in MS Word in some kind of security-related non-editable state, in which your marking ring and word were farther to the left, ringing basically the back lower corner intersection, thus:
I happened to later pick on the "allow editing" button to try zooming in closer, and the marker shifted over to the grids, and the text part included more, thus:
which I would have to assume is what you intended. Who would have guessed there would be a difference like that? But a Word document seems a convoluted way to do this, anyway. If you use the Snipping tool in newer Windows operating systems, or the Print Screen key and paste the result into a graphics editor, and save the relevant portion [no need for the whole screen] as a .gif or .jpg or .png or .tif file, that wouldn't happen. You can mark it up in the Snipping tool itself, if you don't want to do it in the AutoCAD drawing before Snipping. And you can put such an image right in the message body [as I did here] with the misleadingly-named Photos icon, rather than as an attachment that has to be double-clicked on to see.
In any case, HIDE and SHADE and SHADEMODE are still relevant topics to investigate.
Kent Cooper, AIA