✔ 最佳答案
7^(n-1)(7^3-1)/[2X7X7^(n-1)]
=342/14
=171/7
2007-09-07 15:31:32 補充:
TAKE COMMON FACTOR 7^(n-1) from both 分子 and 分母DO THE SIMPLE SIMPLIFICATION.YOU CAN FIND THE ANSWER
2007-09-07 17:19:54 補充:
FIRST,7^(n 1)=7^(n-1)X7 YOU MUST HAVE TO KNOW!!7^(n 2)=7^(n-1)X7^27^(n-1)(7^3-1)/[2X7X7^(n-1)]Since 7^3-1=342, 2X7=14SO 342/14COMMON FACTOR7^(n-1) can be cancelled out
2007-09-07 17:22:29 補充:
IF YOU STILL DO NOT UNDERSTAND, YOU CAN SEND A E-MAIL TO ME,