(2) when 16 < k < 25, q is x? /(25-k)-y？ /( 16-k) = 1, hyperbola.

(3) ellipse a? = 25，b？ = 16-k，

c=√(a？ -B? )=√(25-k- 16+k)=3

Hyperbolic a? = 25，b？ =k- 16

c=√(a？ +b？ )=√(25-k+k- 16)=3

So the focal coordinates are the same.