The answer to the last question on page 18 of seventh grade mathematics published by People's Education Press. (Continue to add points after satisfaction)
(1) The rule you find is -n *n+ 1 =-n +n+ 1 (n is a positive integer).
(2) solution: the original formula =-1+1/2+1/3 minus1/3+1/4+201+20.
=- 1+2065438+ 1/02
= -( 1-20 12)
=-20 12