Equation of motion in the same direction is given by \[{{y}_{1}}=A\sin (\omega t-kx)\], \[{{y}_{2}}=A\sin (\omega t-kx-\theta )\]. The amplitude of the medium particle will be [BHU 2003]

• A.            \[2A\cos \frac{\theta }{2}\]   
• B.            \[2A\cos \theta \]
• C.            \[\sqrt{2}A\cos \frac{\theta }{2}\]                                 
• D.            \[1.2f,\ 1.2\lambda \]