Type Greek letters as well as physics symbols in LibreOffice Impress?

I know Libreoffice Math has a symbol catalog (I believe Libreoffice writer does too) but if copying from those does not work.

Try Ctrl+Shift+U, let go of u but not Shift+Ctrl and type 03A6 (Greek capital letter phi)

The code is ASCII, you can search for what you need here: http://ascii-table.com/unicode-search.php

In Impress menu: Insert > Object > Math. Impress window should now look like Math window. Go to Tools > Catalog and fiddle with symbols. When you're done with Math input menus just click on the background of your slide.

You can also use Insert > Special character but I think it lacks many basic symbols when compared to the method involving Math.

LibreOffice components are integrated. Learn how to use it to your advantage ;)

Add a formula object via main menu → Insert → Object → Formula….

%letter seems to work most simply. For example, I wanted Lambda, so %lambda %delta %theta gives the lower case letters, and %ALPHA or %CHI for their capital versions.