.999… = 1
https://betterexplained.com/articles/a-friendly-chat-about-whether-0-999-1/
https://www.purplemath.com/modules/howcan1.htm
https://polymathematics.typepad.com/polymath/2006/06/no_im_sorry_it_.html
https://www.youtube.com/watch?v=--HdatJwbQY