Consider the ellipse . Let H(α, 0), 0 < α < 2, be a point. A straight line drawn through H parallel to the y-axis crosses the ellipse and its auxiliary circle at points E and F respectively, in the first quadrant. The tangent to the ellipse at the point E intersects the positive x-axis at a point G. Suppose the straight line joining F and the origin makes an angle θ with the positive x-axis.
| List-I | List-II |
|---|---|
| (I) If , then the area of the triangle FGH is | (P) |
| (II) If , then the area of the triangle FGH is | (Q) 1 |
| (III) If , then the area of the triangle FGH is | (R) |
| (IV) If , then the area of the triangle FGH is | (S) |
| (T) |
The correct option is :
Correct Answer :
(I) → (Q); (II) → (T); (III) → (S); (IV) → (P)
Solution :
The correct option is (I) → (Q); (II) → (T); (III) → (S); (IV) → (P).
Let us analyze the geometry of the given problem step-by-step.
The equation of the ellipse is given by:
Comparing this with the standard form , we have:
The auxiliary circle of the ellipse has the radius equal to the semi-major axis . Its equation is:
Let be a point on the auxiliary circle in the first quadrant such that the line joining to the origin makes an angle with the positive x-axis. Thus, the coordinates of are:
Since the line passing through is parallel to the y-axis, the points , , and all share the same x-coordinate, .
Since lies on the x-axis, its coordinates are:
The point lies on the ellipse and has the x-coordinate . In the first quadrant, its y-coordinate is:
Thus, the coordinates of are:
The equation of the tangent to the ellipse at point is:
Substituting and , we get:
Simplifying:
The tangent intersects the positive x-axis at point . Setting , we find:
So, the coordinates of are:
Now, let us calculate the area of . The vertices are:
, , and .
Since the x-coordinates of and are the same, the line segment is vertical (parallel to the y-axis).
The length of the base is:
The height of the triangle is the horizontal distance from to the vertical line :
The area of is:
Now, let us calculate the area for each given value of :
Case (I):
Therefore, (I) → (Q).
Case (II):
Therefore, (II) → (T).
Case (III):
Therefore, (III) → (S).
Case (IV):
We know that:
And:
Substituting these values into the area formula:
Since , we have:
Therefore:
Therefore, (IV) → (P).
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