‘If a+b equals b+a, why is 1/a+b different from 1/b+a?’
Because they're not identically equal 🙄 Welcome to you almost getting the point
ab means a*b
means, isn't equal
That’s why 1/ab=1/(a*b)
Nope, it's because ab==(axb) <== note the brackets duuuhhh!!! 😂
But we could just as easily say 1/ab = (1/a)*b
No you can't! 😂

because that distinction is only convention
Nope! An actual rule, as found not only in Maths textbooks (see above), but in all textbooks - Physics, Engineering, Chemistry, etc. - they all obey ab==(axb)
None of which excuses your horseshit belief that a(b)2
says person still ignoring all these textbooks