I hope you can help me.
I cant understand why periodic function is Time Variant.
Because it does not take the same value for all times.
The definition of periodic means occuring at intervals of time.
In my opinion, a periodic function is a time variant system if the considered time is in the limits of the periodic time constant.
However, since a different input value produces a same output value if the time difference is a multiple of time constant you may consider a periodic function as a "limited time variant”.
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