Equation of motion in the same direction is given by ${\text{y}}_1=\mathrm{Asin}(\mathrm{\omega t}-\mathrm{kx}), {\mathrm{y}}_2=\mathrm{Asin}(\mathrm{\omega t}-\mathrm{kx}-\mathrm{\theta })$. The amplitude of the particle will be 

• A

  $2\mathrm{Acos}\frac{\mathrm{\theta }}{2}$

• B

  $2\mathrm{Acos\theta }$

• C

  $\sqrt{2}\mathrm{Acos}\frac{\mathrm{\theta }}{2}$

• D

  $1.2\mathrm{f},1.2\mathrm{\lambda }$