Observe the following column of numbers: 1 / 2, 1 / 6, 1 / 12, please find out the rule of arrangement and fill in the blanks according to this rule. (1) the ninth number is () the 14th number is
According to the question, 1 / 2 = 1 / (1 * 2), 1 / 6 = 1 / (2 * 3), 1 / 12 = 1 / (3 * 4),
So the ninth number is 1 / (9 * 10) = 1 / 90, and the fourteenth number is 1 / (14 * 15) = 1 / 210