Hi!
I use Abacom's sPlan 8, unfortunately not free tho', (altho' you might be able to use the "demo" version and capture the result as a "screenshot") which you can use to design both the circuit diagram parts and the equations (sPlan 8 has Unicode support so you can use fonts with Greek letters), you can export them as jpeg/bmp or in vector format as svg, which Office 2016 and later can import as one graphic!
If you need root symbols, integral symbols, etc., etc., it's very easy to draw them using line and bezier tools, and then position the equation text to suit – far less aggro than trying to use Word's Equation Editor!
I use "sPlan 8" for all the diagrams in my T & M.Theory and Repair Book I'm writing, and my only connection with Abacom is as a very satisfied user!
I think "XCircuit", which the Chinese often use, and its free, will also do what you need, altho' you may need to design your own root symbols, etc!
Chris Williams