英语周报，2020到2021七年级下册，第33期答案

20.(1)解:设点P(x0,y),由点P到F的距离比点P到x轴的距离大1,可得|PF|=地0+1,1分即y+=y+1,…2分所以p=2,即抛物线C的方程为x2=4y.…………………3分(2)证明:设A(n,y),B(x2,y2),直线AP的斜率为k心,直线BP的斜率为k,则A=2一(x≠x0),km=的一边(x2≠x0)…………………………………5分1-0x2-x0因为直线AP与直线BP的斜率互为相反数,所以kp=一kp,即二边=一边二6分2-x又点A(x,y),B(x2,y)均在抛物线上,可得,化简可得n+x2=-2xo,7分1=x02-0因为x=4,d=4m,所以一a=4y-y2),即二2=+2,…………8分故k9分因为=,所以y=x所以y=x………10分则k=x0.…11分故k+k=012分

第二节One possible versionSuddenly the leader of the boy Scouts stood up and saidMa'am, I think we can help you. He then spent five minutesrearranging his group so that the seats were available for the familyThe boys all followed his directions happily and the mother withthe three children was in relief. She expressed thanks to the boyScouts and the leader with tears in her eyesKallie, however, was beginning to panic at the thought of notbeing next to me. I told her that there wasn't anything I could doWe would have to sit where we were. Amazingly, the man sittingin front of me, turned around to me and asked,Would you andyour daughter like our seats?", referring to himself and his friendHe said he didn't like the window seat and would prefer the aisleWe changed seats and continued our trip, very glad to be togetherand enjoy the scenery from Kallie's window seat. Would that manhave offered us his seat if the Boy Scouts leader hadnt done sofor the mother and her children? I don't know. But I do know thatkindness can affect others

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