作者gs86137 (小飞鱼)
看板trans_math
标题Re: [多变] 极值
时间Fri May 14 19:05:40 2010
※ 引述《gs86137 (小飞鱼)》之铭言：
: Determine the relative extrema and saddle points of
: f(x,y) = x^3 + y^3 + 3xy - 2
我先偏微後变成
fx(x,y) = 3x^2 + 3y
fy(x,y) = 3y^2 + 3x
→ x^2 + y = 0 , y^2 + x = 0
判别式 D(x,y) = fxx‧fyy - (fxy)^2
→ D(x,y) = 36xy - 9
接下来找点要怎麽找呢??
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※ 发信站: 批踢踢实业坊(ptt.cc)
◆ From: 140.128.194.71
1F：推 legstrong:一次微分等於0==>x=y=0或x=y=-1112.105.126.181 05/14 19:31
2F：→ legstrong:分别带入判别式即可112.105.126.181 05/14 19:32
3F：→ gs86137:感谢你搂 140.128.194.71 05/14 21:16
4F：→ gs86137:顺便一问extrema是要求它的local max跟min 140.128.194.71 05/14 23:17
5F：→ gs86137:吗? 140.128.194.71 05/14 23:18