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

• A

  $2\mathrm{A} \cos \frac{\mathrm{\theta }}{2}$

• B

  2A cos $\mathrm{\theta }$

• C

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

• D

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