2022英语周报2高二课标第一期答案

范文Dear jackIve learned with delight that you won the first prize in the U.S. Midwest Chinese Bridge SpeechContest. Please accept my most sincere congratul ati ons and best wishes for a good futureI know how talented you are and how much hard work you' ve made to attain the goal. No onecould be more deserving of the success. And I'm very glad to hear that you owe your success to myhelp and want to study Chinese with me as well. I' m surely willing to give you a hand It's such aat encouragement to me to see your efforts rewarded. Im determined to learn English well, so cayou do me a favor to help me learn English?do hope you can take part in the final contest to be held in China and expect your furtherachievement. Looking forward to he aring from you soonYoursLi Hua范文Dear Jack,I have leaned with delight that you got the first prize in the U.S. Midwest Chinese BridgeSpeech Contest. I would like to extend to you my utmost congratul ations on your suc cess. You mustbe both excited and delighted. And I feel very happy for youIt is quite exciting news. I know this is surely owing to your hard work. It is a reward you richlydeserve. Having you as a friend, I really feel both proud and lucky because I can learn so much fromyou. I wish you would continue to help me with my English, and meanwhile I would be willing tohelp you with your Chinese as well. As we all know, you are a hard-working and talentedperson, which is essential for making achievements. I am sure that I can learn much from you, forwhich I wish you can teach me EnglishI hope that you can take part in the final contest to be held in China. I wish you would continueyour efforts and gain further success in the future. Your success tells me that hard work will pay offn the end. And your example is a constant inspiration to me. I will strug gle to catch up with youMy best wishes to your further success. Congratul ations againYLi Hua

20.解:(1)由题意可得|PF1b23b而由椭圆上的点到左焦点F1的距离的最大值为3可得a+c=3,即a+√a-b=3,∴a-36a+a2,解得a=2,b2=3,∴椭圆C的方程+=1.(2)当直线1垂直x轴时,1:x=0,1:x=2,l1:x=-2,满足OA·OB=-3,但直线l1l2间的距离为,不合题意,舍去当直线1不垂直x轴时,由点M(0,t)(t>0)可设直线l:y=kx+t,且A(x1,y1),B(x2,y2),联立直线l和kx+椭圆C方程组,得{x2,y2,整理得43(3+4k2)x2+8kx+4t2-12=0,则x1+x2=8kt4t2-123+4k3+4k28kt4t2-123+4k2,x1x2=3+4k(又OA·OB=x1x2+y1y2=x1x2+(kx1+t)(kx2+t)=(1+k2)x1x2+kt(x1+x2)+t23,)4t2-12于是有(1+k2)8kt3+4k2+kt3+4k3,解得t=7,…点Mo设直线l1、l2的方程分别为y=kx+m、y=kxy=krtmm,与椭圆联立x2可得43(3+4k2)x2+8kmx+4m2-12=0,于是△=(8km)2-4(4k2+3)(4m2-12)=0,解得m2=4k2+3,而直线l1、l2间的距离为d√k2+1√k2+1杆-3何,解得故直线L的方程为y=士2x

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