Observe the following column: 1 / 2, - 1 / 6,1 / 12, - 1 / 20. Please find out the rule of arrangement and fill in the blanks according to the rule If n is an integer greater than 1, write the nth number according to the above arrangement

Observe the following column: 1 / 2, - 1 / 6,1 / 12, - 1 / 20. Please find out the rule of arrangement and fill in the blanks according to the rule If n is an integer greater than 1, write the nth number according to the above arrangement

The denominator is 1 × 2, 2 × 3, 3 × 4... N × (n + 1)
Sign: positive and negative.. (- 1) ^ (n + 1)
law:
(-1)^ (n+1)/(n×(n+1))