$*$P$16\mathrm{.}2.$ The air$-$gap flux density of a two$-$pole induction motor is given by B$=$Bm cos$($t$$$)$

where Bm is the peak flux density, is the angular displacement around the air gap, and we have assumed clockwise rotation. Give the corresponding expression for the flux density of a four$-$pole induction motor; of a six$-$pole induction motor.