作者GLP (^__________^)
看板trans_math
标题Re: [考古] 96中原医工
时间Thu May 7 00:05:51 2009
※ 引述《lukk790326 (mmmm)》之铭言：
: 不好意思~~可以提示这题如计算吗6. 6. The point on the curve y = x2 that is closest to the point (18,0) is .谢谢
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d = √(x-18)^2 + y^2
令M = (x-18)^2 + y^2 = (x-18)^2 + x^4
dM
-- = 4x^3 + 2x - 36 = 2(x-2)(2x^2 + 4x + 9) = 0 => x=2 为临界点
dx
d^2 M
-----| = 12*4 > 0
dx^2 |x=2
当x=2时有极小值272 ,最短距离为 √272 ,
(x,y) = (2,4)
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