设等比数列{an}的各项均为正数,其前n项和为Sn.若a1=1,a3=4,Sk=

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问题:

设等比数列{an}的各项均为正数,其前n项和为Sn.若a1=1,a3=4,Sk=63,则k=______.

考点:等比数列的通项公式等比数列的前n项和
题型:填空题

A total of 4.6 million digital televisions have been sold, and the sales of HDTV sets have quadrupled since last year. Consumers have bought HDTVs to play their DVDs and to have clearer pictures and wide screens. Only a small percentage of the people who have purchased HDTVs, however, have actually hooked their TVs up to receive high-definition television digital signals. Perhaps television viewers are having trouble keeping up with the changes in technology. Even the manufacturers of HDTVs, like Mitsubishi, Thomson Multimedia, Sony, and Samsung seem to have a tough time learning how to make their sets work with the various digital TV formats because little standardization has been required or implemented in the industry.
Some of the HDTVs Weigh over 200 lbs., and a variety of retailers offer a delivery service to the buyer’s home to help install the heavy sets. This is known as a white-glove service and usually comes with an extra fee. After HDTV purchasers get their sets home and hook them up, they will still need to Work to get the digital signals to their systems. Most of the industry’s cable providers do not yet offer high-definition programing, and only about 15% of commercial television stations have switched over to even the lowest improved digital pictures. Worse yet, viewers may need to install antenna before they can even get the digital signals to their new HDTV sets. Another frustration for home-theater seekers is that the current HDTV sets allow owners only to watch high-definition programs, not to record them.

On the whole, this passage is positioned to dwell on______.

A.the overall picture of the HDTV sector

B.how the giant TV makers should offer better products

C.a lament over consumers’ inability to use a high-end TV set

D.a criticism of the.TV makers for doing nothing about a big problem

题型:填空题

子宫颈口有部分性胎盘覆盖()

A.正常胎盘

B.边缘性前置胎盘

C.完全性前置胎盘

D.部分前置胎盘

题型:填空题

海盐生产中通常用()来表示海水(卤水)的浓度。

A.设施表

B.浓度表

C.波美度

D.盐度表

题型:填空题

出洗涤塔工艺原料气温度偏高将会导致原料气()增加。

A.带水

B.带碳黑

C.带二氧化碳

D.带一氧化碳

题型:填空题

常用来制造一般机器零件,如轴承、齿轮、凸轮轴等的塑料是()。

A.高压聚乙烯

B.尼龙

C.聚甲醛

D.ABS

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