5.24. If the probability is f (x) that a product fails the xth time it is being used, that is, on the xth trial, then its fail- ure rate at the xth trial is the probability that it will fail on the xth trial given that it has not failed on the rst x 1 trials; symbolically, it is given by where F (x) is the value of the corresponding distribution function at x. Show that if X is a geometric random vari able, its failure rate is constant and equal to 9