Problems with the tangent plane

Question 4

Consider the function f(x,y)=(1/y-x)

Use GraphTan to plot the tangentplane to this function at (x0,y0)=(1,0).

Why won't it plot? What is the geometric significance of this?

Question 5

Consider the sphere from question 2:

F(s,t)=(cos(s)cos(t), sin(s)cos(t), sin(t)), s=0..2*Pi,t=0..2*Pi

Use the ParamTan command to plot the tangent plane at (s0,t0)=[0,Pi/2]

Why is there no plane at the point? What does this mean geometrically?

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