Suppose that we have a random variable X and its pdf is as follows: at?\" for) = x+1' 9 5 I 0, otherwise where a :> 0 and 9 :> 0. Note a and 6' are the population parameters. IfX1,X2, ...,Xn is a random sample from this distribution and 9 is xed (you can treat 6' as a constant and no need to estimate it), please nd the maximum likelihood estimator for a