[填空题]
An automobile engine slows down fr25j vy/a 8gn ;wjkhes(s*, dfu5*1r4 wotaihm om 4500 rpm to 1200 rpm in z p2/ jfl1 mz.+v.ub3(zney;ge2kp rh 2.5 s. Calculate (a) its angular acceleration, assumed constant, $rad/s^2$ (b) the total number of revolutions the engine makes in this time. $rev$