The speed of wave is depedant only on the wavelength and frequency of waves since it is given by s=fw where s is the speed, f is frequency and w is the wavelength. Since the options given has only one factor, that is frequency, hence option D is correct. In case we had wavelength could be among the options, both would be correct.
Let t = Theta and p = Phi Tan t = y/x Then x =y/Tant. Tant = y/(x-d) x-d = y/Tanp y/Tant - d = y/Tanp y -d*Tanr = y*Tant/Tanp y-y*Tant/Tanp = d*Tanr y(1 - Tanr/Tanp = d*Tant
