Cannot Add PPA Behind Proxy Ubuntu 14.04 [duplicate]
You need to export your proxy environment variables using
export http_proxy=http://username:password@host:port/
export https_proxy=https://username:password@host:port/
and then tell sudo to use them using:
sudo -E add-apt-repository ppa:webupd8team/y-ppa-manager
or open your /etc/sudoers file (using sudo visudo) and append
Defaults env_keep="https_proxy"
to the end of the file.
I have a blog on this, have a look at it for more details.