π: Ctrl+P or
Alt+P or pi.
∞: Ctrl+8
or Alt+8 or infinity.
θ: Ctrl+T or
Alt+T or theta. You can also use x or t instead of θ in polar mode; they will be
replaced by θ when you press Draw Graph or Enter on the keyboard.
The quickest way to type domain= (-infinity, infinity) is by deleting the domain entirely (including domain=) and pressing Enter.