we can draw lines measuring angles from 3'o clock..but how to draw two lines at an angle when we don't know angle from 3'o clock?? we only know angle between lines but not the angle of line starting from 3'o clock.

Hello mrd33p, if I understand your needs if you type the command line , enter , clic to start your line , @100<45 you will obtain a line length 100 with an angle of 45° from the horizontal.
@ is to define a coordinate in relation with your first clic, if you type 100<45 you will draw a line length 100 with an angle of 45° from the horizontal but starting from the coorfdinate 0,0.
Hope this will help you.
Ask for more.philippe JOSEPH2014-12-03 10:16:51

thanks philippe JOSEPH,but I don't want the angle to start from horizontal,say, I have drawn first line at an unknown angle with horizontal, and now I want to draw another line aligned with first line at an angle of 45 how can I do that ?

Aligned?  Don't you mean relative to the angle of the first line that was drawn?Read this.  I like the reply by nestly the best.http://forums.autodesk.com/t5/autocad-2010-2011-2012/drawing-angled-lines-relative-to-the-angle-of-another-line/td-p/2829683
John Connor2014-12-03 18:33:30

Hello again mrd33p, for me a simple way do do this would be to clic on the line to be copied at a certain angle to "light" the grips and clic on the grip at the "center" of the angle and with right clic select rotation , copy and the angle to be between the 2 lines.If the line is at the right angle but not at the right place you can move it by the conventional command MOVE or clic on the middle grip and move it with your mouse.This method is called "working with the grips".Hope this will help.
philippe JOSEPH2014-12-03 18:40:44

Also known as "grip editing" which is the method suggested by nestly (and demonstrated in a video he linked to) in the link that I provided.  I guess great minds think alike.

thank you all :)I did it.... its your win