If you have ever wondered how to open an application using terminal, the command is very simple.
> open -a application_name
> open -a Calculator.app
Note that auto-complete will place a forward slash like this
> open -a Calculator.app/
You will have to remove it. Your current directory in terminal should be the Applications folder as well. If it isn’t, you’ll have to specify it in the path. eg if you are in your home directory:
> open -a /Applications/Calculator.app