英语周报 2018-2022 七年级 课24答案

第二节One possible version:I recalled the lad s words. I thought it was time to pay her kindness forward, by buying the twomen a meal and two cups of coffee to thank them for all that they had done. So I paid the bill and wrotedown my blessings as well as"paying it forward"on the back of the bill. The firefighters were confused atfirst, but upon listening to me explaining everything, they accepted my offer pleasantly. After their mealthey left gratefully and joyfullOne of the firefighters posted the picture of the bill online and explained his ex perience in therestaurant. The post has since gained the attention of social media users all over the world, receivingcountless shares and likes in less than three days. Many people shared their stories in the comment sectionabout how they "pay it forward"and a lot more people decided to follow my example to do the goodpractice just as we did. viewing those heartfelt comments, I realized that by helping others, we can starta chain of reaction of positive feeling and good deeds that can benefit our whole society.

(1)由题意得f(x)=-e2+--a,x>0,令g(x)=∫(x)则g(x)=-e2-在(0,+∞)上递增,且g'(1)=0xe(0,1)时,g'(x)<0,g(x)递减:当x∈(1+∞)时,g'(x)>0,g(x)递增g(x)ns=g(1)=2-a<0g-|=e>0.g(1)=2-a<0,∴玉=,1g(x)=0当x∈(0,x)时,g(x)=f(x)>0f(x)递增当x∈(x1)时,g(x)=f"(x)<0,∫(x)递减,x=石是f(x)的极大值点g(+ha)=1+in>0g(1=2-a<0.:31+a).g()=0当x∈(1,x2)时,g(x)=f(x)<0,f(x)递减当x∈(x2,+∞)时,g(x)=∫(x)>0.f(x)递增,x=2是f(x)的极小值点.∴∫(x)在(0,+a)上有两个极值点(2)证明:由(1)得 0,1互 2)则(a)=--1<0,∴(a)在a>2时单调递减,则a(a)<9(2)=1n2-1<01+na

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