2022英语外研版周报天津答案

短文改错As an exchange student, I must admit that atfirst America was a big culture shock for me. I staystavewith a host family in a small town. My host parents organized a lot of activities in my spare time such that Iwouldnt miss home but feel lonely. However, life was hardly to get used A. My main problem was over theornartothwItlanguage. I failed to understand many in the first few weeks because everyone spoke so fast and used a lot ofmuchidioms. Food was another difference. Their host family always had bread, potatoes and salad for mealIs. I reallyMymiss dumplings, rice and delicious dishdishes

19.【解析】(1)△A1AB和△A1AC中,由余弦定理求得:A1B=A1C=√7,2分取BC中点为E,则A1E⊥BC由A1E=A1B2-BE=6,又AE=√3故△A1EA中,AE+AE=AA1…∴∠A1EA=90°,即A1E⊥AE4分又A1E⊥BC,且BC∩AE=E,可得:A1E⊥平面ABC5分A1EC平面A1BC,∴平面A1BC⊥平面ABC分(2)设点A到平面BCC1B1的距离为dB1到平面ABC的距离等于A1到平面ABC的距离,而A1到平面ABC的距离为A1E=√6,则B1到平面ABC的距离为6故VB-=3,6·S6x=3·6·3=2,………………………8分9分又BC⊥A1E,BC⊥AE→BC⊥平面A1AE,故BC⊥AA1→BC⊥BB1,则S△B1xC=210分V,4x=V→3a,Sm=,即号×d×3==d一故点A到平面BCC1B1的距离为√212分

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