求1+2+22+23+…+22012的值，可令S=1+2+22+23+…+220_爱下问搜题

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问题选择题

求1+2+2²+2³+…+2²⁰¹²的值，可令S=1+2+2²+2³+…+2²⁰¹²，则2S=2+2²+2³+2⁴+…+2²⁰¹³，因此2S-S=2²⁰¹³-1．仿照以上推理，计算出1+5+5²+5³+…+5²⁰¹²的值为（　　）

A．5²⁰¹²-1

B．5²⁰¹³-1

C．

52013-1

4

D．

52012-1

4

答案

设S=1+5+5²+5³+…+5²⁰¹²，则5S=5+5²+5³+5⁴+…+5²⁰¹³，

因此，5S-S=5²⁰¹³-1，

S=

52013-1

4

．

故选C．

补全对话，情景问答

从方框中选择合适的句子补全对话。

A. Is that for here or to go
B. And here's your change
C. May I help you
D. Do you want anything to drink with that
E. That comes to three dollars and thirty cents please

A: Welcome to Burger Town. 1_______?
B: Yes. I'd like a hamburger and an order of French fries .
A:  2_______.
B: Yes. I'll have a cup of coffee.
A: OK. That's a hamburger, an order of French fries , and a cup of coffee.  3_______?
B: For here.
A: 4_______.
B: Here you are.
A:  5_______  Your food will be ready in a moment.

报关编码

金属粉末，按重量计含银96。5%，含金2。0%，含铂1%，含钯0。5%()