2022英语周报，七年级，答案

书面表达One possible versionI求Dear PeterI heve good news for you Our school Food Club will hold a dumpling- making activity. As you're interestedin Chinese food, I'm writing to invite you to join in the activity with me.As a kind of traditional Chinese food, dumplings are very popular during festivals, especially in the SpringFestival, when people will get together to make dumplings. The activity will begin at g am next Saturday in theschool canteen. First, (chefs) will teach us how to make dumplings step by step. Then, there will be a dumplingmaking competition in groups. Finally comes the most exciting part--enyoying our dumplings.Looking forward to your coming.Your

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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