Answer: 
Explanation:
A direct proportionality means a linear relationship between two variables and rate of change means an application of derivatives. Hence, the mathematical model is:

Frequency = velocity/wavelength
Frequency = 10/20
Frequency = 0.5 Hz
Answer:

Explanation:
We know that impedance of a RLC circuit is given by 
So
here R is resistance
is inductive reactance and
is capacitive reactance
To minimize the impedance
should be zero we know that 
So 


We know that 
So 

Where f is resonance frequency