Explanation

(b) Given $\ :y_{1} = 4\sin{404\pi t,\ y_{2} = 3\sin{400\pi t}}$
$\therefore\omega_{1} = 404\pi,\omega_{2} = 400\pi,A_{1} = 4,\ A_{2} = 3$
$\omega_{1} = 2\pi v_{1} \Rightarrow 404\pi = 2\pi v_{1} \Rightarrow v_{1} = 202\ Hz$
$\omega_{2} = 2\pi v_{2} \Rightarrow 400\pi = 2\pi v_{2} \Rightarrow v_{2} = 200\ Hz$
Beat frequency $= v_{1} - v_{2} = 202 - 200 = 2\ Hz$
$\frac{I_{\max}}{I_{\min}} = \left( \frac{A_{1} + A_{2}}{A_{1} - A_{2}} \right)^{2} = \left( \frac{4 + 3}{4 - 3} \right)^{2} = \left( \frac{7}{1} \right)^{2} = \frac{49}{1}$