The sphere S intersects with the plane П → x = a gives the circle
C→y2+z2=b2
S→∣∣p−p0∣∣=r
with
r=abb2+a2
p=(x,y,z),p0=(x0,y0,z0)
x0=a+r2−b2,y0=z0=0
Consider the line L→p=λv which passes by (0,0,0)
intersections S and L:
∣∣λv−p0∣∣=r
λ2∣∣v∣∣2−2λ⟨v,p0⟩+∣∣p0∣∣2=r2
λ=⟨v,p0⟩±⟨v,p0⟩2−∣∣v∣∣2(∣∣p0∣∣2−r2)
the line L must be tangent to S hence
⟨v,p0⟩2−∣∣v∣∣2(∣∣p0∣∣2−r2)=0
This is the locus defining the cone surface.
Putting v=(x,y,z) and applying the values for p0,r we get
b4x2−a4(y2+z2)−2a2b2(y2+z2)+a2b2(x2+y2+z2)=0
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