[考古] 90中央化工
Consider the function f(x,y,z)=4(x^2+y^2)-z^2
The surface defined by f(x,y,z)=0 is a cone.
Find the unit normal vector on the surface of
the cone f(x,y,z)=0 at the point P,whose coordinate is(1,0,2)
答案是 正負5^(-1/2)<2,0,-1>
我是想問為什麼有正負?
因為有的類似題目答案只有正的
是什麼時候正負才要寫出來??
謝謝~
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