To achieve the same, add the CEWP to the page, where you do not want to display the Quick Launch. Open Source Editor of CEWP and add the following
Once the above <style> has been added, go to Advance Setting, set “Audience Targeting”. Set the group/audience to which you do not want to display the Quick Launch bar.
I have set the “Visitors” group in Audience Targeting. This setting will not allow the “Visitors” to see the Quick Launch bar.
I have a moss_user1 in Visitors Group and moss_user2 in Members Group.