If the vertex of a hyperbola bisects the distance between its centere ...
Given: The vertex of a hyperbola bisects the distance between its center and the corresponding focus.
To find: The ratio of the square of its conjugate axis to the square of its transverse axis.
Solution:
Let the hyperbola be of the form $\frac{x^2}{a^2}-\frac{y^2}{b^2}=1$.
Let the center of the hyperbola be $(0,0)$.
Let the distance between the center and the focus be $c$.
Let the vertex of the hyperbola be $(0,\pm a)$.
Then, the foci of the hyperbola are at $(0,\pm c)$.
Given that the vertex bisects the distance between the center and the focus, we have:
$$\frac{c}{2}=a$$
Solving for $c$, we get:
$$c=2a$$
The distance between the vertices of the hyperbola is $2a$.
The distance between the endpoints of the conjugate axis is $2b$.
Therefore, the ratio of the square of the conjugate axis to the square of the transverse axis is:
$$\left(\frac{2b}{2a}\right)^2=\left(\frac{b}{a}\right)^2$$
Substituting $c=2a$ in the equation of the hyperbola, we get:
$$\frac{x^2}{a^2}-\frac{y^2}{b^2}=1 \Rightarrow \frac{x^2}{a^2}-\frac{y^2}{a^2-c^2}=1$$
Substituting $c=2a$, we get:
$$\frac{x^2}{a^2}-\frac{y^2}{a^2-4a^2}=1 \Rightarrow \frac{x^2}{a^2}-\frac{y^2}{-3a^2}=1$$
Therefore, $a^2=3b^2$.
Substituting this in the ratio of the square of the conjugate axis to the square of the transverse axis, we get:
$$\left(\frac{b}{a}\right)^2=\left(\frac{1}{\sqrt{3}}\right)^2=\frac{1}{3}$$
Therefore, the answer is option D, 3.