3,9,27,81……..531441中有多少个术语?
(A) 25
(B) 12
(C) 13
(D) 14答案: (B)
解释:
3, 9, 27, 81..............531441 form a G.P.
with a = 3 and r = 9/3 = 3
Let the number of terms be n
根据公式,
GP的第N个项表示为T n = axr n-1
Then 3 x 3n-1 = 531441
∴ 3n = 312
∴ n = 12
这个问题的测验