GWD-26-Q8

nicboy

    

Q8:

    

In the sequence 1,
2, 4, 8, 16, 32, … , each term after the first is twice the previous term.  What is the sum of the 16th, 17th, and 18th
terms in the sequence?

    

 

    

A.  2¹⁸

    

B.  3 (2¹⁷)

    

C.  7 (2¹⁶)

    

D.  3 (2¹⁶)

    

E.  7 (2¹⁵)

    

Answer: E

为什么是E， 我选D

rosemary99

等比数列求和：第16，17，18项分别为2^15,2^16,2^17,

所以和为2^15(1+2+2^2)=7(2^15)

Ambitiouseye

先列出通项：2^(n-1)

再算