Thevenin's Theorem: AC Circuits with Different Frequencies

[Vishera]

My textbook has this excerpt:

I am not sure why it refers to Example 10.6 as that is unrelated. I don't understand to be honest. How can you calculate the Thevenin equivalent at different frequencies? Let us say that you have two voltage source: v₁(t)=10cos(5t) and v₂(t)=10cos(2t). So how do you calculate the Thevenin equivalent at the first frequency of 5 Hz? Do you change v₂'s frequency to 5 Hz?

 

[psparky]

I think they mean when you use superposition, you use the voltage source you're intersted in and short the other one.

You will then have two different circuits, each with it's own voltage source and frequency.

Then when you go to find your open circuit voltage...you will end up with two different open circuit voltages with two different frequencies from two different sources. You cannot add different frequencies together.

One open circuit voltage will contain (5t) and the other open circuit voltage wil contain (2t).
You would never interchange these like you suggested and also the 5 in 5t is not hertz...it's 5 radians per second...

Just my first guess...or 2nd or third...