问题
选择题
设x，y满足条件
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答案
解：不等式表示的平面区域如图所示阴影部分，
当直线ax+by=z（a＞0，b＞0）过直线x-y+2=0与直线3x-y-6=0的交点（4，6）时，目标函数z=ax+by（a＞0，b＞0）取得最大12，
∴4a+6b=12，即2a+3b=6，
∴
当且仅当
时，
的最小值为4
故选D．
搜题请搜索小程序“爱下问搜题”
设x，y满足条件
|
解：不等式表示的平面区域如图所示阴影部分，
当直线ax+by=z（a＞0，b＞0）过直线x-y+2=0与直线3x-y-6=0的交点（4，6）时，目标函数z=ax+by（a＞0，b＞0）取得最大12，
∴4a+6b=12，即2a+3b=6，
∴
当且仅当 时，的最小值为4
故选D．
(2013·东北三省四市联合诊断考试)I had a bad habit of skipping to the last pages of a book.I just wanted to see how it ended ____ I was still in the middle of it. This habit ____ first my mom，then my friends, and ____ even my own daughter. Often my ____ wouldn't be limited just to the books I read but also to what others were ____ as well.Then one day my daughter told me in anger, “Dad, please just read a book one ___ at a time like everyone else！” At times I didn't ___ this bad habit to just books either.I also tried to skip ahead in my own life and ____ out what to do months and even years from now ____ enjoying each day at present. Although I knew that the ____ of my life wasn't done yet and that I had many pages ___ to go, I still couldn't control my burning desire to write the ____ of it halfway through.Time and again, I would ____ jump ahead and try to solve every potential problem before it happened. Life，____，doesn't work like that.It loves to ____ us，and you never know what new problems, changes, or opportunities each new day will ____. Recently when I found myself living in the ____ again，I felt a voice that gently told me I needed to “live one day at a time”. When I heard those words, I ____，turned the book of my life back to the ____ page, and thanked God for today. Each of us has to ____ the book of life line by line，moment by moment and trust that our story will be brought to its perfect end.
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