2017 2018英语周报高一答案

2.解:(1)令F(x)=x 2=x2 2,则F(x)=21分令F(1,得x=13分因为F(1)=3,所以切线l的方程为y=x 分(2)A G()=2f(r) ag(r)=2efl-(a 2)xtaln rta则G(x)=2 2e1-(a 2)=(a 2)x当x≥1时,f(x)=e-1-1≥0,故f(x)在[1, ∞)上单调递增所以f(x)≥f(1)=0,即e≥x,2x2-(a 2)x a(2x-a)(x-1)所以G(x)≥①当a≤2时,G(x)≥0在[1, ∞)上恒成立,即G(x)在[1, ∞)上单调递增因为G(x)≥G(1)=0,所以a≤2满足题意8分②当a>2时,令H(x)=G(x)=a 2c-1-(a 2),则H(x)=- 2c1,因为H(x)在[1, ∞)上单调递增且H(1)=2-a<0,H(G)=2e-1-1>0所以H(x)在(1,a)上存在唯一的零点x0当x∈[1,xo)时,H(即H(x)在(1,x0)上单调递减,此时H(x)≤H(1)=0,则G(x)在(1,x)上单调递减,此时G(x)

第一节One possible versionDear Ms JenkinsI'm writing to ask you for help. Our school is going to sponsor an exhibition of Chinese paintings in theschool library next month. As president of the student council, i have been assigned the job of drafting an arnouncement in English as there aredreds of international students in our schoohave already written a rough draft of the above-mentioned announcement. But I'm afraid that there aresome mistakes in the English language. So I am hoping you would correct my possible mistakes in the announce-ment that i have attachedId appreciate it if you could do me the favocerely yourLIH

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