(1)等式a(n-1)/an=[2a(n-1)+1]/(1-2an)可化为：a(n-1)-an＝4an·a(n-1)两边同除以an·a(n-1)得：1/an－1/a(n-1)＝4所以{1/an}为等差为4的等差数列,首项1/a1＝51/an＝1/a1+4(n-1)＝4n+1an＝1/(4n+1)(2)a1＝1/5,a2＝1/...