[DSE 2020] 同學仔開始溫你嘅 數學 未？ [2]

No

btw 想知你講既呢類係咩series

做咩唔訓

去廁所

呢類係個人覺得比較特別嘅GS
你拆晒啲括號就會見到
(2^n)x - (2^(n-1))x - (2^(n-2))x - ... - x
第2個term開始就係一條GS (r=2)
問題係呢條式唔容易搵
你要靠pattern自己去guess
2-x, 4-3x = 2^2 - 2x - x,
8-7x = 2^3 - (2^2)x - 2x - x etc

2^n - (2^(n-1))x - (2^(n-2))x - ... - x
打錯sorry

成條全中再請多餐

ci = 1/20？

No..

我唔知係咪篤錯機，9/20？

唔係喎😨

ai 1/2
aii 1/6
b 61/36
ci 1/4
cii 6/85

冇野了，寫左條式出黎都篤錯，

點解係(1+10%)/(1+5%)

End of 2015:
P(1+5%)
2015舊錢, 1次息

End of 2016:
P(1+5%)(1+5%)
+ P(1+10%)(1+5%)
2015舊錢, 2次息
+ 2016舊錢, 1次息

End of 2017:
P(1+5%)(1+5%)(1+5%)
+ P(1+10%)(1+5%)(1+5%)
+ P(1+10%)(1+10%)(1+5%)
2015舊錢, 3次息
+ 2016舊錢, 2次息
+ 2017舊錢, 1次息

P(1+10%)(1+5%)(1+5%)
除 P(1+5%)(1+5%)(1+5%)
= (1+10%)/(1+5%)

P(1+10%)(1+10%)(1+5%)
除 P(1+10%)(1+5%)(1+5%)
= (1+10%)/(1+5%)

所以ratio係(1+10%)/(1+5%)
(你可以試埋2018)

最尾唔岩

2/29？

Yes

終於篤岩機

弱弱一題

(a) 2^n + n
(b) 2^20 + 99
出得好

sorry (b)計錯
(2/3)(2^20 - 1) + 100