2022英语周报高二38课标答案

Li hua第二节参考范文But Alex uxs shocked to see a crocodile swimming in a jar of pickles. The crocodile looked mean andappeared ready to attack. Alex closed the refrigerator door and cried out, "Help me! Please help me! "Alex'sry for help woke everyone in his family up. His parents and brother rushed to see what was wrong. Alex hidbehind the kitchen table as he pointed to the refrigerator and said, " Daddy, there s a crocodile in our pickle jar.Alex's Dad reached into the pickle jar and took a huge bite out of the crocodile. It was just a piece of pickleThen Aler's parents reminded him of how important food was for energy. Alex's empty stomachwhy he had felt dizzy and weak: and when you feel that way your eyes can play tricks on you. So you see.never was a crocodile in the pickle jar that night! The next evening when Alexs Mom told everyone there wasplenty of leftover chocolate cake for dessert, Alex was the only one who didnt want any. He was too full.Three helpings of vegetables will do that.

10.(1)证明:因为an an 2=A 2an 1,a1=a2=1,所以a3=2a2-a1 A=A 1,a4=2a3-a2 A=3 1,a5=2a1-a3 A=6A 1,又因为a4-a1=3A,a5-a4=3入,所以a4-a1=a5-a4,故a1,a4,a5成等差数列(2)H antang=n 2a11,a 2-antI=anti-anth令b,=an 1-an,则bn 1-b=A,又b1=a2-a1=0,所以{bn}是以0为首项,A为公差的等差数列,故bn=b1 (n-1)A=(n-1)A,即an 1-an=(n-1)入,所以an 2-an=2(an 1-an) 入=(2n-1),所以所以Sn当A=0时,Sn=n,当λ≠0时,Sn=2 2 224(1-22)所以数列(cn}的前n项和为S,=2(1-22)(3)不存在理由如下:由(2)知an 1-an=(n-1)λ,用累加法可求得an=1 (n-1)(n-2)入(n≥2),当n=1时,也适合上式,所以假设存在三项a, 1-1,a1 1-1,ap 1-1成等比数列,且s,t,p也成等比数列,则(a1 1-1)2=(a, 1-1)(a 1-1)t2(t-1)2s(s-1)p(p-1)4因为s,t,p成等比数列,所以t2=s,所以(t-1)2=(s-1)(p-1),化简得s p=2t,联立t2=sp,得s=t=p这与题设矛盾故不存在三项a1-1-1,a1 1-1,ap 1-1成等比数列,且s,t,p也成等比数列

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