題目:http://i18.photobucket.com/albums/b128/silver_sylvia/008007.jpg
solution:http://i18.photobucket.com/albums/b128/silver_sylvia/IMG345.jpg
唔好意思幅圖唔係咁清...佢hence想搵個lim(x->infinity)x(n)
我個問題其實只係同b part個limit有關..
我想問下點解要用呢個方法?
有冇得解係點樣諗到用呢個方法既呢?
因為我望住佢我會明但我唔知佢係點諗出黎既....
同埋我唔明佢第2去到第3步個rhs....
點解會變左個fraction?
係咪用左geometric sequence條sum既formula?
因為ce既野我唔記得左啦-_-
唔該哂各位高人!!