JAMIA MILLIA ISLAMIA Jamia Millia Islamia Solved Paper-2008

  • question_answer
        The ellipse\[\sec \theta =m\]and\[\tan \theta =n,\]the hyperbola\[\frac{{{x}^{2}}}{25}-\frac{{{y}^{2}}}{16}=1\]have in common

    A)  centre only

    B)  centre, foci and directrices

    C)  centre, foci and vertices

    D)  centre and vertices only

    Correct Answer: D

    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\[e\]be the eccentricities of the ellipse and hyperbola. \[\therefore \]  \[e=\sqrt{\frac{{{a}^{2}}-{{b}^{2}}}{{{a}^{2}}}}=\sqrt{\frac{25-16}{25}}\]                 \[=\frac{3}{5}\] and        \[e=\sqrt{\frac{{{a}^{2}}+{{b}^{2}}}{{{a}^{2}}}}=\sqrt{\frac{25+16}{25}}\]                 \[=\frac{\sqrt{41}}{5}\] (i) Centre of ellipse is (0, 0) and centre of hyperbola is (0, 0). (ii) Foci of ellipse are\[(\pm ae,0)\]or\[(\pm 15,0)\]foci of hyperbola are\[(\pm ae,0)\]or\[(\pm \sqrt{41},0)\]. (iii) Directrices of ellipse are\[x=\pm \frac{a}{e}\] \[\Rightarrow \]\[x=\pm \frac{25}{3}\]directrices of hyperbola are\[x=\pm \frac{a}{e}\] \[\Rightarrow \]               \[x=\pm \frac{25}{\sqrt{41}}\] (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 in centre and vertices.


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