JEE Advanced 2008 · Paper 1 · Mathematics · Ellipse
Let P (x_1, y_1) and Q(x_2, y_2), y_1 < 0, y_2 < 0 , be the end...
Let P\left(x_1, y_1\right)andQ(x2,y2),y1<0,y2<0, be the end points of the latusrectum of the ellipse x2+4y2=4. The equations of parabolas with latusrectum PQ are
Options
Ax2+23y=3+3
Bx2−23y=3+3
Cx2+23y=3−3
Dx2−23y=3−3
Correct answer
B. x2−23y=3+3
Step-by-step solution
The equation x2+4y2=4 represents an ellipse with 2 and 1 as semi-major and semi-minor axes and eccentricity 23. Thus, the ends of latusrect are \left(\sqrt{3}, \frac{1}{2}\right)and(3,−21),(−3,−21)and(3,−21).<imgsrc="/api/proxy−image?url=httpsAccordingtothequestion,weconsideronlyP \left(-\sqrt{3},-\frac{1}{2}\right)andQ \left(\sqrt{3},-\frac{1}{2}\right).
Now, PQ=2\sqrt{3}
Thus, the coordinates of the vertex of the parabolas are A(0,2−1+3) and A^{\prime} \left(0, \frac{-1-\sqrt{3}}{2}\right) and corresponding equations are and
(x-0)^2=-4 \cdot \frac{\sqrt{3}}{2}\left(y+\frac{1-\sqrt{3}}{2}\right)
i.e.,(x-0)^2=4 ⋅23\lleft(y−2−1−3)and
x2+2\ssqrt3y=3−3x2−2\ssqrt3y=3+3