Hi everyone. So I'm typing up some notes for some high school kids I'm helping with their math (I'm not tutoring them for money, I'm helping them informally). I want to put diagrams in my notes, you know the usual stuff: graphs of the usual functions; explaining concepts in diagrams; geometry diagrams etc. Do you know of any programs that can allow me to draw such diagrams, and gives professional-looking results? Publication-worthy diagrams? Any free programs? There's quite a lot of kids I could help, and I don't have the time to be there and draw diagrams for them and explain stuff etc., which is why I'm asking for programs that produce good graphics. If I'm reeeeaaaally picky, can they be user-friendly too please?