2022英语周报八年级 新目标 9答案

第一节【参考范文】Dear annieIm Li Hua. Hows everything going these days? I'd like to ask you to write an article for our schools English newspaperThe"Culture field "section is very popular among us students. And here are some relevant details about the articles we areeager for. Would you please write something about how Americans spend their holidays and festivals, which is interesting andinformative? 400 words would be fine. Could we have your article before June 10?I'm looking forward to your replySincerely yoursLi Hua

4.B【关键能力】本题考查逻辑思维能力【解题思路】作出不等式组表示的平面区域及直线x-2y=0,平移该直线,数形结合可知当平移后的直线过直线x y-3=0与x-y 1=0的交点A时,z=x-2y取得最小值,即可得解【解析】作出不等式组表示的平面区域如图中阴影部分所示,作出直线x-2y=0并平移数形结合可知当平移后的直线经过直线x 2y0y-3=0与x-y 1=0的交点A时z=x-2y取得最小值.由得lx-y 1=0,y=2所以A(1,2),所以zn=1-2×2=-3结论拓展》求线性目标函数z=ax by(ab≠0)的最值,当b>0时,直线z=x by过可行域内的点且在y轴上截距最大时,z最大在y轴上截距最小时,z最小;当b<0时,直线z=ax by过可行域内的点且在y轴上截距最大时,z最小,在y轴上截距最小时,z最大

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