✔ 最佳答案
1)數列通項是T(n)=k/n,若t(12)=1/3,求k的值
代 n = 12, T(12) = k/12 = 1/3
k/12 = 1/3
k = 4
2)數列通項是T(n)=4n-20
a)數列有多少項是負數?
T(n)=4n-20 ∠ 0是否數列的其中一項
4n ∠ 20
n ∠ 5
其實
T(1) = 4(1) - 20 = -16
T(2) = 4(2) - 20 = -12
T(3) = 4(3) - 20 = -8
T(4) = 4(4) - 20 = -4
T(5) = 4(5) - 20 = 0
T(6) = 4(6) - 20 = 4
所以, 有4項是負數
b)求兩個連績項的差
T(n+1) - T(n)
= [4(n+1)-20] - [4(n)-20]
= 4n + 4 - 20 - 4n + 20
= 4
c)7788是否數列的其中一項
代 T(n) = 4n - 20 = 7788
4n = 7788 + 20 = 7808
n = 7808 / 4 = 1952
即7788是數列的第1952項