[考古] 台聯96第二題
In what direction is derivative of f(x,y)=(x^2-y^2)/(x^2+y^2) at P(1,1)
equal to zero?
先找出f(1,1)的向量=i-j
另u=u1i+u2j為和f(1,1)垂直單位方向
(i-j)內積(u1i+u2j)=0
u1-u2=0 u1=u2 取u1=u2=1/根號2
故在(1/根號2 , 1/根號2)方向
我的問題是 取u1=u2=1/根號2 這段我有點看不懂=.=
有沒有高手可以幫我解釋一下@@ 感謝
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