Question

化简式子求值

｛1／（n＋3）×n｝＋｛1／（n＋3）（n＋3＋3）｝＋｛1／（n＋3＋3）（n＋3＋3＋3）｝
／是分数线
过程加结果

Answer 1

原式=1/3[1/n - 1/(n+3)]
+ {1/3[1/(n+3) - 1/(n+6)]}
+{1/3[1/(n+6)- 1/(n+9)]}
化简=1/3n - 1/(n+9)
=3/n(n+9)

Answer 2

｛1／（n＋3）×n｝＋｛1／（n＋3）（n＋3＋3）｝＋｛1／（n＋3＋3）（n＋3＋3＋3）｝
=(1/3)×[1/n-1/(n+3)+1/(n+3)-1/(n+6)+1/(n+6)-1/(n+9)]
=(1/3)×[1/n-1/(n+9)]
=(1/3)×9/n(n+9)
=3/(n²+9n)