Let a sequence (an)n-1,2,3,... satisfy J a = 3 ak+1 Then, a -4ak +5 (k = 1, 2, 3,...). (1) (1), a and generally, an = (5) x (6) (5) (2), 93 Caution: The answers should be written in integers or fractions. (2) (6) (3) n E (3), a4 +(7) (n = 1,2, 3, ...). (4)