How to find fundamental frequency of two signals?

Question

I am facing difficulty with finding fundamental frequency of signals

I mean by fundamental frequency=(1/Time period)

Correct me if I am wrong

consider two continuous time signals with Time period of signal “a”=T1 frequency =f1 (

Time period of signal “b”=T2 frequency =f2=nfo : m and n are cofactor

Then, fundamental frequency of

a+b                         HCF of two frequencies f1 and f2
multiplication of a and b   Don’t know how to proceed
convolution of a and b      LCM of two frequencies f1 and f2

fo is lcm of two frequencies.

Plz also elaborate procedure if any for such equations.