© SE Production Limited 14 All Rights Reserved 2021 9 . The random variable X has the probability density function 3 2 1 ( ) 1 x f x e e � � � , 1 3 x � � . ( a ) Write down the mode . [ 1 ] ( b ) Show that the exact value of the median is 2 1 3 ln 2 e � � � � � � � � . [ 4 ]