3)If the random variable T is the time to failure of a commercial product and the values of its probability density and distribution function at time "t" are f(t) and F(t), then its failure rate at time t is given by f(t) / 1-F(t)

Thus, the failure rate at time t is the probability density of failure at time t given that failure does not occur prior to time t.
a)show that if t is an exponential distribution, the failure rate is constant.
b)show that if T has a weibull distribution thae failure rate is given by (alpha*beta)*t^beta-1