F.1 math (general term of sequence)

4,-16,64,-256...
Starting from the second term, each term is -4 times of the previous term and the general term is
-(-4n)
(Because the first number, 4, is positive and it's equal to -(-4))

2008-10-13 17:49:58 補充：
sorry
The answer is -(-4)^2

2008-10-13 17:50:19 補充：
nonono
-(-4)^n

4,-16,64,-256...

T(2)/T(1)=-16/4=-4
T(3)/T(2)=64/-16=-4
So 4,-16,64,-256... is a geometric sequence

The first term a=4
The common ratio r=-4

The General term T(n):
ar^(n-1)
=4(-4)^(n-1)
=-(-4)(-4)^(n-1)
=-(-4)^n