J & K CET Engineering J and K - CET Engineering Solved Paper-2005

  • question_answer
    If the foci of an ellipse are \[(\pm \sqrt{5},0)\] and its eccentricity is \[\sqrt{5}/3,\] then the equation of the ellipse is

    A)  \[9{{x}^{2}}+4{{y}^{2}}=36\]

    B)  \[4{{x}^{2}}+9{{y}^{2}}=36\]      

    C)  \[36{{x}^{2}}+9{{y}^{2}}=4\]

    D)  \[9{{x}^{2}}+36{{y}^{2}}=4\]       

    Correct Answer: B

    Solution :

    Given, eccentricity \[e=\frac{\sqrt{5}}{3}\] and  foci \[=(\pm \sqrt{5},\,0)\] \[\Rightarrow \] \[ae=\sqrt{5}\] \[\Rightarrow \] \[a=\frac{\sqrt{5}\times 3}{\sqrt{5}}=3\] Now, \[{{b}^{2}}={{a}^{2}}(1-{{e}^{2}})=9\left( 1-\frac{5}{9} \right)\] \[\Rightarrow \] \[{{b}^{2}}=4\] \[\therefore \] The equation of ellipse is \[\frac{{{x}^{2}}}{{{a}^{2}}}+\frac{{{y}^{2}}}{{{b}^{2}}}=1\] \[\Rightarrow \] \[\frac{{{x}^{2}}}{9}+\frac{{{y}^{2}}}{4}=1\] \[\Rightarrow \] \[4{{x}^{2}}+9{{y}^{2}}=36\]


You need to login to perform this action.
You will be redirected in 3 sec spinner