To install Go 1.9 on Ubuntu 16.04, first add the PPA and install the golang-1.9-go package:
sudo add-apt-repository ppa:gophers/archive
sudo apt update
sudo apt-get install golang-1.9-go
The add go the go path to the your PATH:
echo "export PATH=$PATH:/usr/lib/go-1.9/bin" >> ~/.profile
Then finally load the new path:
source ~/.profile
Although everything should now work, it might be wise to just log out and back in to make sure other programs also get the updated path.