8. Recall that the ("raw" ) moments of a random variable X are E[X* ] for k = 1, 2, 3, .... Write /k = E[Xk]. (a) Describe the first two moments (i.e. /1, /2) qualitatively. If X is measured in "meters", what are the units of /k? (b) The central moments of X are defined by ak = E[(X - E[X])*]. Describe the first two central moments (i.e. a1, 02) qualitatively. (c) Express /4 in terms of /, a1, a2, a3, a4