A photon of wavelength $\;\lambda\;$ is scattered from an electron , which was at rest .The wavelength shift $\;\bigtriangleup \lambda\;$ is three times of $\;\lambda\;$ and the angle of scattering $\;\theta\;$ is $\;60^{0}\;$ . The angle at which the electron recoiled is $\;\phi\;$ .The value of $\;tan \phi\;$ is : (electron speed is much smaller than the speed of light)
