作者keith291 (keith)
看板trans_math
标题Re: [考古] 数题考古题
时间Thu Mar 26 21:07:01 2009
※ 引述《darkstar0412 (目标当个米虫废物公务员)》
: 4.y=2x-10 ,find the values for xand y such that thier product is a minimun.
y=2x-10
=>(y+10)/2=x
=>(y^2+10y)/2 =xy
=>xy=(y^2+10y)/2 ={(y+5)^2-25}/2 >= -25/2
等号在y=-5时成立 代入 y=2x-10 得x=5/2
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1F：推 darkstar0412:感谢....不过看不懂Orz 220.134.79.28 03/26 21:47
2F：→ darkstar0412:懂了 刚刚一时脑残^^ 220.134.79.28 03/26 21:51
3F：推 ElvinN:原来是如此!我英文太差了Orz 118.165.92.252 03/26 22:10