This is very simple: Step 1: First, break the left form into the following: (a/(x+1))+(b/(x-2));

Step 2: Total grade, (a/(x+1))+(b/(x-2)) = (a (x-2)+b (x+1))/((x+1)

Step 3: compare the universal molecule with the original molecular formula;

(A+B)X+B-2A= 1, equation: a+b = 0; 2A= 1

B= 1/3，A=- 1/3

Generally, both factors do this, and the above is the general practice. If the three factors are different, the above method is also used, but if the factors are different, the method will change.