Consider a wideband PM signal produced by a sinusoidal

Consider a wideband PM signal produced by a sinusoidal modulating wave Am cos (2pA?mt), using a modulator with a phase sensitivity equal to k p radius per volt.
(a) Show that if the maximum phase deviation of the PM signal is large compared with one radian, the bandwidth of the PM signal varies linearly with the modulation frequency A?m.
(b) Compare this characteristic of a wideband PM signal with that of a wideband FM signal.