Answer:
Option B
Explanation:
$f_{A}= 1430 [\frac{330}{330-2\cos\theta}]$
$= 1430 [\frac{1}{1-\frac{2\cos\theta}{330}}]\approx 1430[1+\frac{2\cos \theta}{330}]$
[ from binomial expansion]
$f_{B}=1430[\frac{330}{330+1\cos\theta}]$
$\approx1430[1-\frac{\cos \theta}{330}]$
Beat frequency = $f_{A-}-f_{B}$
$=1430[\frac{3\cos \theta}{330}] =13\cos\theta$
$=13[\frac{5}{13}] =5.00 Hz$