英语周报高一外研20202021第7期答案

Paragraph 1A seat beside her was empty, and Dannis occupiedHe ielt a wave of anger swept over him. "Where is mywallet?"he yelled. The black-haired girl glanced up fromher reading, with a confused look on her face. Dannis stoodup, glared at her and shouted, "You stole my wallet! "Thecrowds began to gossip. The girl turned deadly palelooking so restless that words failed her. A strange silencehung in the air. Abruptly, she leaped from the seat.Paragraph 2:The girl ran and Dannis ran after her. After awhile, Dannis finally grabbed her by the arm. At exactlyhat moment, a policeman approached them and askedbout what happened. Dannis hastened to explain it whilethe girl frowned with a shake of her head. After furtherenquiries, the policeman took out a wallet and banded it toDannis,adding that someone had found it in the toiletWhat a mistake he had made! Overwhelmed byyDannis made an apology to thegirl.

20.解:(1)据题意知,点(2,1)在抛物线C:x2=2py上所以2=2p×1,解得p=2所以抛物线C的标准方程是x2=4y证明:(2)据(1)求解知,抛物线C的方程为y=1x2所以y=5x5分设点D(x),则直线的斜率Ax一6分因为点A与点D关于y轴对称所以有点7分设E(x,x),B(=,),则1x-n+一号m,即x+x=2x因为kA10分所以k+km=2+2=+2二2=0即直线AB的斜率与直线AE的斜率之和为定值12分

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