1, with a score of less than 0, b greater than 0 and c greater than 0; B is less than 0, A is greater than 0, and C is greater than 0; C is less than 0, A is greater than 0, and B is greater than 0; If abc is less than 0, the four results are-1+1+1=1; 1- 1+ 1= 1; 1+ 1- 1= 1; - 1- 1- 1=-3

2. The sum of absolute squares cannot be negative. If the sum is 0, ab-2=0, 1-a=0. Is this the first step to solve the problem? A = 1，B = 2。

The value of the second step is11* 2+1/2 * 3+1/3 * 4 ...+1/212 *.

= 1- 1/20 13=20 12/20 13