Explanation:
The beat frequency is given by :
[tex]\omega_{beat}=|\omega_1-\omega_2|[/tex]..........(1)
[tex]\omega=\dfrac{2\pi}{T}[/tex]
Where
T is the time period
Equation (1) becomes :
[tex]\dfrac{2\pi}{T_{beat}}=\dfrac{2\pi}{T_1}-\dfrac{2\pi}{T_2}[/tex]
[tex]\dfrac{1}{T_{beat}}=\dfrac{1}{T_1}-\dfrac{1}{T_2}[/tex]
[tex]\dfrac{1}{T_{beat}}=\dfrac{T_2-T_1}{T_1T_2}[/tex]
[tex]T_{beat}=\dfrac{T_1T_2}{T_2-T_1}[/tex]
So, the correct option is (a) "[tex]T_{beat}=\dfrac{T_1T_2}{T_2-T_1}[/tex]". Hence, this is the required solution.