點用式求第幾項？

First: The equation is wrong. This equation is used to find sum to n term (When first term and the last is known).

Used another method:

Ans:

T(n) = a + (n - 1)d
a = 35
d = 32 - 35 = - 3
T(n) = 2
n = ?

2 = 35 + (n - 1)(- 3)

- 33 = - 3n + 3

- 36 = - 3n

3n = 36

n = 12

３５，３２，２９．．．．．２　

ａ＝３５　ｄ＝３　Ｎ＝？　
Ｔ（１）＝３５
Ｔ（Ｎ）＝２

N=[(35-2)/3]+1
=33/3+1
=12