Q93 / 180 · COMEDK 2016 · Mathematics
The ellipse $\frac{x^{2}}{25}+\frac{y^{2}}{16}=1$ and the hyperbola $\frac{x^{2}}{25}-\frac{y^{2}}{16}=1$ have in common
- Correct answerAcentre and vertices only
- Bcentre, foci and vertices
- Ccentre, foci and directrices
- Dcentre only
Solution
Equation of ellipse is
$\frac{x^{2}}{25}+\frac{y^{2}}{16}=1, a>b$
and equation of hyperbola is
$\frac{x^{2}}{25}-\frac{y^{2}}{16}=1, a>b$
Let $e$ and $e^{\prime}$ be the eccentricities of the ellipse and hyperbola.
So,
$e=\sqrt{\frac{a^{2}-b^{2}}{a^{2}}}=\sqrt{\frac{25-16}{25}}=\frac{3}{5}$
and $\quad e^{\prime}=\sqrt{\frac{a^{2}+b^{2}}{a^{2}}}=\sqrt{\frac{25+16}{25}}=\frac{\sqrt{41}}{5}$
(i) Centre of ellipse $(0,0)$ and centre of hyperbola is $(0,0)$
(ii) Foci of ellipse are $(\pm a e, 0)$ or $(\pm 3,0)$. Foci of hyperbola are $\left(\pm a e^{\prime}, o\right)$ or $(\pm \sqrt{41}, 0)$.
(iii) Direction of ellipse are
$x=\pm \frac{a}{e} \Rightarrow x=\pm \frac{25}{3}$
and directrices of hyperbola are $x=\pm \frac{a}{e}$
$\Rightarrow \quad x=\pm \frac{25}{\sqrt{41}}$
(iv) Vertices of ellipse are $(\pm a, 0)$ or $(\pm 5,0)$. Vertices of hyperbola are $(\pm a, 0)$ or $(\pm 5,0)$.
From the above discussions, their are common is centre and vertices.
Hence, the correct answer is option: 'A'.