Two waves having equation <br> $x_1 = a \sin (\omega t + \phi_1)$ <br> $x_2 = a \sin (\omega t + \phi_2)$ <br> If in the resultant wave the frequency and amplitude remains equals to amplitude of superimposing waves. Then phase diff. between them :-

Question

( A ) $\frac{\pi}{4}$
( B ) $\frac{\pi}{6}$
( C ) $\frac{2\pi}{3}$
( D ) $\frac{\pi}{3}$