17.(10分)(1)解:若选①在△ABC中,由正弦定理可得:ABsn∠ACB=sn∠BAC1分又3AB=4BC,in∠ACB=2可得:sin∠BAC=1,∴∠BAC=……………3分又AB⊥AD所以∠BAD=2,所以∠DAC=3;4分(Ⅱ)在△ACD中,DC=2,由余弦定理可得:DC=4=AC+AD2-AC·AD≥AC·AD分即AC·AD≤48分∴Sc=2AC· ADsin/DAC≤2×4x210分当且仅当AC=AD时取“若选②(I)由tan(∠BAC+x)=√3可得:∴∠BAC2分又AB⊥AD所以∠BAD=5,所以∠DAC=3;………………………………4分(Ⅱ)在△ACD中,DC=2,由余弦定理可得:DC=4=AC+AD2-AC·AD≥AC·AD…………………………………………6分即AC·AD≤4………8分∴S△c=AC· ADmin∠DAC≤×4×=√310分当且仅当AC=AD时取“=”若选③(I)2 BCos∠ACB=2AC-3AB,由正弦定理得2sin∠ BACco∠ACB=2sin∠ABC-√3sin∠ACB…………………………………1分2sin∠ BACco∠ACB=2sin(∠ACB+∠BAC)-√3in∠ACB可得:cos∠BAC=,所以∠BAC=x,…3分又AB⊥AD所以∠BAD=2,所以∠DAC=34分(Ⅱ)在△ACD中,DC=2,由余弦定理可得:DC=4=AC2+AD2-AC·AD≥AC·AD即AC·AD≤4…………分分∴SAc=AC· ADsi∠DAC≤×4×y0=310分当且仅当AC=AD时取“=”

一缺乏话句间的连接成分,内容不连贯。信息未能传达给读者。0分未能传达给读者任何信息:内容太少,无法评判:写的内容均与所要求内容无关或所写内容无法看清。(yy) One Possible VersionDear PeterLearning that you want to know the National College Entrance Examination(NCEE)in ourprovince, I'm writing to tell you about it.NCEE is the biggest examination in China, which means a great deal to every Chinesestudent. On one hand, it is the only way to attend a college. On the other hand, it determineswhat job one can obtain in the future. Generally speaking, it usually takes place on 7-8 Juneevery year. Chinese, maths and foreign languages are the required exam subjects. The studentsof arts and science can choose other three subjects according to their willFor me, Peking University is my favorite university, which is the ideal university for mostChinese students

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