(1) 3 9 -3 0
2 4 -2 0
-3又1/7 9又1/49 3又1/7 0
-2 4 2 0
9/27 84/27² -9/27 0
(2) n n² -n 0
n²÷(-n)+n=0
(3) n²÷(-n)+n=0
=-n+n
= 0