2022英语周报高一英语下学期答案

书面表达One possible version:NOTICEA sports meeting will be held in the playground of our school from next Thursday to FridayAs you know, the pressure of study is very heavy now, especially for those senior 3. So the purpose of the sports meeting is to letevery student get relaxed, as a result of which we students can live happily and heal thilyEveryone is welcome to take part in it. Those who perform excellently at the sports meeting will get prizes. But don' t take theresults so serously because taking part is more important than the result. Good luck to everyone!

19.【解析】(1)取AB1的中点G,联结BG,FG,F、G分别是AB、AB1中点,∴FG∥BB1,FG=BB1,又∵FG∥EC,FG=EC∴四边形FGEC是平行四边形,∴CF∥EG.∵CF￠平面AEB1,EGC平面AEB1,∴CF∥平面AEB1(2)以C为坐标原点,射线CA,CB,CC为xy,z轴正半轴,建立如图所示的空间直角坐标系C-xyz则C(0,0,0),A(2,0,0),B1(0,2,4).8分A设E(0,0,m),平面AEB1的法向量n=(x,y,z),E则AB=(-2,2,4),AE=(-2,0,m),且AB⊥n,AE⊥nAB1·n=-2x 2y 4z=0,所以2x 0y mz=0,取z=2,则n=(m,m-4,2),三棱柱ABC一A1B1C1是直棱柱,∴BB1⊥平面ABC,又∵ACC平面ABC,∴AC⊥BB1,∵∠ACB=90°∴AC⊥BC,BB1∩BC=B,∴AC⊥平面ECBB1…∴CA是平面EBB1的法向量,CA=(2,0,0),二面角A-EB1-B的大小是45°则√2C|·|nl2xvm (m-4)2 2z,解得m5,2m∴在棱CC1上存在点E,使得二面角A一EB1-B的大小是45°,此时CE=512分

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