a1=1/1*3=1/2*(1-1/3) a2=1/3*5=1/2*(1/3-1/5) a3=1/5*7=1/2*(1/5-1/7) a4=1/7*9=1/2*(1/7-1/9) 按以上规律列出第五等式a5=______________求a1+a2+a3+a4+a5+.+a2012的值.快 时间有限
显然an=1/[(2n-1)(2n+1)]a5=1/(9*11)=(1/2)(1/9-1/11)a1+a2+a3+a4+a5+.+a2012=(1/2)(1-1/3+1/3-1/5+……+1/5)=(1/2)(1-1/4025)=
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扫描下载二维码已知等差数列{an}的各项均为正数 求证：1/(√a1+√a2)+1/(√a2+√a3)+……+1/(√an-1+√an)=（已知等差数列{an}的各项均为正数 求证：1/(√a1+√a2)+1/(√a2+√a3)+……+1/(√an-1+√an)=（n-1）/(√a1+√an)
1/(√an-1+√an)=(√an-1-√an)/(√an-1+√an)(√an-1-√an)=-1/d(√an-1-√an)
d为等差数列{an}的的公差左边=-1/d(√a1-√a2+√a2-√a3+……+√an-1-√an）
=-1/d(√a1-√an)
=(√an-√a1)/d
= (an-a1)/d(√a1+√an)
=(n-1)/(√a1+√an)=右边所以
原等式成立
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扫描下载二维码这是个机器人猖狂的时代，请输一下验证码，证明咱是正常人~IS61DDP2B42M36A/A1/A2 (ISSI) PDF技术资料下载
IS61DDP2B42M36A/A1/A2 供应信息 IC Datasheet 数据表 (1/32 页)
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IS61DDP2B42M36A/A1/A2
4Mx18 ， 2Mx36 72MB DDR- IIP （连拍4 ） CIO同步SRAM
[4Mx18, 2Mx36 72Mb DDR-IIP(Burst 4) CIO SYNCHRONOUS SRAM]
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4Mx18 ， 2Mx36 72MB DDR- IIP （连拍4 ） CIO同步SRAM[4Mx18, 2Mx36 72Mb DDR-IIP(Burst 4) CIO SYNCHRONOUS SRAM]
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&&&&ISSI [ INTEGRATED SILICON SOLUTION, INC ]
IS61DDP2B44M18A/A1/A2IS61DDP2B42M36A/A1/A24Mx18, 2Mx3672Mb DDR-IIP(Burst 4) CIO SYNCHRONOUS SRAM(2.0 Cycle Read Latency)FEATURES?????????????????2Mx36 and 4Mx18 configuration available.On-chip Delay-Locked Loop (DLL) for wide datavalid window.Common I/O read and write ports.Synchronous pipeline read with self-timed late writeoperation.Double Data Rate (DDR) interface for read andwrite input ports.2.0 cycle read latency.Fixed 4-bit burst for read and write operations.Clock stop support.Two input clocks (K and K#) for address and controlregistering at rising edges only.Two echo clocks (CQ and CQ#) that are deliveredsimultaneously with data.+1.8V core power supply and 1.5V to 1.8V VDDQ,used with 0.75 to 0.9V VREF.HSTL input and output interface.Registered addresses, write and read controls, bytewrites, data in, and data outputs.Full data coherency.Boundary scan using limited set of JTAG 1149.1functions.Byte write capability.Fine ball grid array (FBGA) package:13mm x 15mm & 15mm x 17mm body size165-ball (11 x 15) arrayProgrammable impedance output drivers via 5xuser-supplied precision resistor.Data Valid Pin (QVLD).ODT (On Die Termination) feature is supportedoptionally on data inputs, K/K#, and BWx#.The end of top mark (A/A1/A2) is to define options.IS61DDP2B42M36A : Don’t care ODT functionand pin connectionIS61DDP2B42M36A1 : Option1IS61DDP2B42M36A2 : Option2Refer to more detail description at page 6 for eachODT option.ADVANCED INFORMATIONJULY 2012DESCRIPTIONThe 72Mb IS61DDP2B42M36A/A1/A2 andIS61DDP2B44M18A/A1/A2 are synchronous, high-performance CMOS static random access memory (SRAM)devices. These SRAMs have a common I/O bus. The risingedge of K clock initiates the read/write operation, and allinternal operations are self-timed. Refer to theTimingReference Diagram for Truth Tablefor a description of thebasic operations of these DDR-IIP (Burst of 4) CIO SRAMs.Read and write addresses are registered on alternating risingedges of the K clock. Reads and writes are performed indouble data rate.The following are registered internally on the rising edge ofthe K clock:?Read/write address?Read enable?Write enable?Byte writes?Data-in for first and third burst addresses?Data-out for first and third burst addressesThe following are registered on the rising edge of the K#clock:?Byte writes?Data-in for second and fourth burst addresses?Data-out for second and fourth burst addressesByte writes can change with the corresponding data-in toenable or disable writes on a per-byte basis. An internal writebuffer enables the data-ins to be registered one cycle afterthe write address. The first data-in burst is clocked one cyclelater than the write command signal, and the second burst istimed to the following rising edge of the K# clock. Two fullclock cycles are required to complete a write operation.During the burst read operation, the data-outs from the firstbursts are updated from output registers of the second risingedge of the K clock (starting two cycles later after readcommand). The data-outs from the second burst are updatedwith the third rising edge of the K# clock where readcommand receives at the first rising edge of K.The device is operated with a single +1.8V power supply andis compatible with HSTL I/O interfaces.????Copyright (C) 2010 Integrated Silicon Solution, Inc. All rights reserved. ISSI reserves the right to make changes to this specification and its products at any timewithout notice. ISSI assumes no liability arising out of the application or use of any information, products or services described herein. Customers are advised toobtain the latest version of this device specification before relying on any published information and before placing orders for products.Integrated Silicon Solution, Inc. does not recommend the use of any of its products in life support applications where the failure or malfunction of the product canreasonably be expected to cause failure of the life support system or to significantly affect its safety or effectiveness. Products are not authorized for use in suchapplications unless Integrated Silicon Solution, Inc. receives written assurance to its satisfaction, that:a.) the risk of injury or damagb.) the user a andc.) potential liability of Integrated Silicon Solution, Inc is adequately protected under the circumstancesIntegrated Silicon Solution, Inc.- Rev. 00A7/05/20121【求详解,内详】设{an}是各项均为正数的递增的等比数列,且a1+a2+a3=14/3,1/a1+1/a2+1/a3=21/8设{an}是各项均为正数的递增的等比数列,且a1+a2+a3=14/3,1/a1+1/a2+1/a3=21/8（1）求数列{an}的通项公式（2）前n项和Sn
a1+a2+a3=a1(1+q+q^2)=14/3 (1)1/a1+1/a2+1/a3=1/a1*(1+1/q+1/q^2)=1/a1*(q^2+q+1)/q^2=21/8 (2)(1)/(2)得(a1q)^2=16/9则a2=4/3a1+a2+a3=a2(1/q+1+q)=14/3则q=1/2或q=2a1=4或2/3an=4*(1/2)^(n-1)或2/3*2^(n-1)（2）前n项和Sn 用公式sn=a1*(1-q^n)/(1-q)
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