2022 英语周报 九年级 LDX 28答案

取小121.(1)解:依题意,f(x)=x2-x-2=(x+1)(x-2)令f(x)>0,解得x<-1或x>22分故函数f(x)的单调增区间为(-∞,-1)和(2,+∞),单调递减区间为(-1,2)4分(2)证明:设F(x)=2f(x)+ax+(x2+x)lnx+b则F(x)=2x2+2(1-a)x-a+(2x+1)hnx+(x2+x)=(2x+1)(nx+x+1-a)因为x∈(0,+∞),令F(x)=0,得hx+x+1-a=0分令h(x)=lnx+x1a,由丁h(x)在(0上单调递增当x→0时,h(x)→-∞;当x→++∞时,h(x)→+∞0故存在唯一x0∈(0,+∞),使得h(x0)=0,则a=x0+lnxo+1分当0 x0时,F(x)>0,故F(x)在(x0,+∞)上单调递增当x∈(0,+∞)时,F(x)m=F(x0)=(+x0)nx0+x+(-x-nxo)2-(xo+nxo+1)xo+b-1-x-x0+b,故一支x--0+b≥0,即b≥1x++x,则b-2a≥3x+x3+x0-2a=3x+x5-x0-2nxo-210分设x)=32+x2-x-2hx-2,x∈(0,+∞),故9(x)x3+2x2-x-2(x-1)(x2+3x+2当0 1时,g(x)>011分故当x∈(0,+∞)时,9(x)m=y1)=3故b-2a-512分即3b-6a+5

第四部分写作第一节短文改错事Offering help is always a good tradition in ourcountries. It is believed that by heelp anothercountnhelpingperson, you are helping yourself. Helping others dodohave a significant effect on a person's happiness. Eventhough we usually feel the urge A compete with othertotaktime to assist otherseneficial to us. Besides, helping people is a goodbenefitway to build trust, particular if you never expect orparticularldemand something to be given to you in retum.anythingNowadays, a rising number of individaIs areready to assist tht others. This has resulted from awonderful community, which people live in harmonynIwherewith each other

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