Please show briefly how to find the general term of the following sequences:
a. 1, -2, 3, -4, 5, -6, .........
b. 4, 7, 11, 18, 29, 47, 76, .........
S1 Sequences
2006-11-04 7:40 am
回答 (4)
2006-11-04 7:48 am
✔ 最佳答案
a) a[0] = 1, a[n] = (-1)^(n-1) * a[n-1]+1 for all n >= 1即係個 sequence 係 1,2,3,4 咁去.. 只係逢雙數係負數...
b) a[0] = 4, a[1] = 7, a[n] = a[n-2] + a[n-1] for all n >= 2
即係由第三個數開始，係由之前o個兩個數加埋...
11 = 4 + 7
18 = 7 + 11
29 = 11 + 18
...
2006-11-09 2:45 am
a.７
b.１２３
b.１２３
2006-11-04 7:57 am
a.f(1)=1=1x(-1)^0
f(2)=-2=2x(-1)^1
f(3)=3=3x(-1)^2
f(4)=-4=4x(-1)^3
so f(n)=n(-1)^n-1
b.this is the Fibonacci Sequence
f(1)=4
f(2)=7
f(3)=f(1)+f(2)=4+7=11
f(4)=f(2)+f(3)=7+11=18
so f(n)=f(n-2)+f(n-1)
f(2)=-2=2x(-1)^1
f(3)=3=3x(-1)^2
f(4)=-4=4x(-1)^3
so f(n)=n(-1)^n-1
b.this is the Fibonacci Sequence
f(1)=4
f(2)=7
f(3)=f(1)+f(2)=4+7=11
f(4)=f(2)+f(3)=7+11=18
so f(n)=f(n-2)+f(n-1)
參考: me
2006-11-04 7:48 am
Qa.
分2組睇: 1, 3, 5, 7,9.....
-2, -4, -6, -8, -10........
所以 Ans 係: 1, -2, 3, -4, 5, -6, 7, -8, 9, -10, 11, -12.......
Qb.
4+7 =11
7+11 =18
11+ 18 = 29.....
so Ans is: 4, 7, 11, 18, 29, 47, 76, 123, 199......
明唔明???
分2組睇: 1, 3, 5, 7,9.....
-2, -4, -6, -8, -10........
所以 Ans 係: 1, -2, 3, -4, 5, -6, 7, -8, 9, -10, 11, -12.......
Qb.
4+7 =11
7+11 =18
11+ 18 = 29.....
so Ans is: 4, 7, 11, 18, 29, 47, 76, 123, 199......
明唔明???
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