JEE Advanced2008MathematicsEllipseActual
Let P (x₁, y₁ ) and Q (x₂, y₂ ), y₁ < 0, y₂ < 0 , be the end points of the latusrectum of the ellipse x^2+4 y^2=4 . The equations of parabolas with latusrectum P Q are
Options
- Ax^2+2 3 y=3+ 3
- Bx^2-2 3 y=3+ 3
- Cx^2+2 3 y=3- 3
- Dx^2-2 3 y=3- 3
Correct answer
B. x^2-2 3 y=3+ 3
Step-by-step solution
The equation x^2+4 y^2=4 represents an ellipse with 2 and 1 as semi-major and semi-minor axes and eccentricity 3 2 . Thus, the ends of latusrect are ( 3 , 1 2 ) and ( 3 ,- 1 2 ), (- 3 ,- 1 2 ) and ( 3 ,- 1 2 ) . According to the question, we consider only P (- 3 ,- 1 2 ) and Q ( 3 ,- 1 2 ) . Now, P Q=2 3 Thus, the coordinates of the vertex of the parabolas are A (0, -1+ 3 2 ) and A^ (0, -1- 3 2 ) and corresponding equations are and (x-0)^2=-4 3 2 (y+ 1- 3 2 ) i.e., (x-0)^2=4 3 2 (y- -1- 3 2 ) and aligned & x^2+2 3