I was wondering if it's possible to create these relatively basic shapes from the primary geometric shapes (i.e. polygons and ellipses - particularly circles, squares, and triangles).
You don't necessarily have to use Illustrator, that's just what I use (pathfinder, shape builder, boolean operations, etc.). It's probably more related to geometry and tech drawing with a straight edge & compass than anything.
These were done relatively freehand and by tracing curves with the pencil & pen/Bézier curve tools. None came out perfectly symmetrical, so I split them down the middle, and paired the best half of each one with its mirror image.