说明了稳定状态失业率是U/L=s/（s+f)。假设失业率开始时并不在这个水平。说明失业率将一直变动并达到这种稳定

说明了稳定状态失业率是U/L=s/(s+f)。假设失业率开始时并不在这个水平。说明失业率将一直变动并达到这种稳定状态。(提示：把失业人数变动作为s，f和U的函数。然后说明，如果失业高于自然失业率，失业下降；如果失业低于自然失业率，失业增加。)

In this chapter we saw that the steady-state rate of unemployment is U/L=s/(s+f). Suppose that the unemployment rate does not begin at this level. Show that unemployment will evolve over time and reach this steady state. (Hint: Express the change in the number of unemployed as a function of s,f, and U. Then show that if unemployment is above the natural rate, unemployment falls, and if unemployment is below the natural rate, unemployment rises.)