What is the recursive rule for this geometric sequence? 320, 80, 20, 5, ... Responses a1=1280; an=14an1 a subscript 1 end subscript equals 1280 semicolon a subscript n end subscript equals 1 fourth a subscript n minus 1 end subscript a1=320; an=4an1 a subscript 1 end subscript equals 320 semicolon a subscript n end subscript equals negative 4 a subscript n minus 1 end subscript a1=320; an=14an1 a subscript 1 end subscript equals 320 semicolon a subscript n end subscript equals 1 fourth a subscript n minus 1 end subscript a1=1280; an=4an1