How can I separate or extract varying frequency components from a signal?

For example, I have a f = f1 + f2 + f3 where, f1 = sine wave signal of 50 Hz, f2 = some unknown harmonics components, f3 = a varying frequency component from 5 to 15 Hz.

I want to extract the frequency component f3 (whose frequency is varying) from the whole signal f.

Note: I don't know the details about unknown harmonics. What kind of adaptive filtering technique can be used? I don't want to remove f3 but to get f3 with frequency probably 5-15 Hz

Answer 1

[Abhishek Ballaney]

https://in.mathworks.com/help/matlab/ref/fft.html

[Jan Kubski]

Thank you for the comment Abhishek. Actually I don't want to use FFT for this.

The more detailed question I have asked again in this link. https://www.mathworks.com/matlabcentral/answers/377554-how-can-i-separate-or-extract-varying-frequency-components-from-a-signal