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第一节短文改错（每小题1分，共10分）We have an radio club in our school,which A started two years ago.I am lucky as I'm one of theawashost.Our club is much more than just music.Every morning we broadcast the weather,the recentlyhostsrecentnews and some special messages.During exam time,we had a special program to tell students thathavewhat they should do for preparation.In the end of the school year,many students whom are graduatingAtwhouse our club to give messages to your teachers and close friends.When parents come to our school,wetheiroften play songs sang by the students and inform them of some important events.sung

17.【解析】审题指导(1)a}是公比不为a,为a2,aa1,2,y设公比关于g的一1的等比数列的等差中项关系式为q元二次方程(a的公比2)由(1)及a,得到{na}的前n错位相{na}的{a}通项公式项和表达式减法求和前n项和解：(1)设{an}的公比为q,由a1为a2,a的等差中项，得2a1=a2+a3,"2分即2a1=a19+a19.所以g2+q-2=0,解得g=1(舍去)，9=-2.4分故{an}的公比为-2.6分(2)记S。为{nan}的前n项和由(1)及a,=1可得，an=(-2)-1,则nan=n·(-2)m-1所以Sn=1+2×(-2)+…+n×(-2)-1,…7分-2Sn=-2+2×(-2)2+…+(n-1)×(-2)"-1+n×(-2)".9分两式相减可得3Sn=1+(-2)+(-2)2+…+(-2)"--n×(-2)”1-（-2)"3-nx(-2).[点拨]将1+(-2)+…+(-2)m-1看作首项为1，公比为-2的等比数列，求其前n项和11分1(3n+1)(-2)”所以Sn=12分99