JEE Main 2008 — Coordinate Geometry

A parabola has the origin as its focus and the line $x=2$ as the directrix. Then the vertex of the parabola is at

The point diametrically opposite to the point $P(1,0)$ on the circle $x^2+y^2+2 x+4 y-3=0$ is

A focus of an ellipse is at the origin. The directrix is the line $x=4$ and the eccentricity is $1 / 2$. Then the length of the semi-major axis is

The perpendicular bisector of the line segment joining $P(1,4)$ and $Q(k, 3)$ has $y$-intercept - 4. Then a possible value of $k$ is