Question Details

Consider the ellipse x24+y23=1. 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-IList-II
(I) If θ=π4, then the area of the triangle FGH is(P) (31)48
(II) If θ=π3, then the area of the triangle FGH is(Q) 1
(III) If θ=π6, then the area of the triangle FGH is(R) 34
(IV) If θ=π12, then the area of the triangle FGH is(S) 123

(T) 332

The correct option is :

Options

A

(I) → (R); (II) → (S); (III) → (Q); (IV) → (P)

B

(I) → (R); (II) → (T); (III) → (S); (IV) → (P)

C

(I) → (Q); (II) → (T); (III) → (S); (IV) → (P)

D

(I) → (Q); (II) → (S); (III) → (Q); (IV) → (P)

Show Answer

Correct Answer :

Option C

(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:
x24+y23=1
Comparing this with the standard form x2a2+y2b2=1, we have:
a2=4a=2
b2=3b=3

The auxiliary circle of the ellipse has the radius equal to the semi-major axis a=2. Its equation is:
x2+y2=4

Let F be a point on the auxiliary circle in the first quadrant such that the line joining F to the origin makes an angle θ with the positive x-axis. Thus, the coordinates of F are:
F(2cosθ,2sinθ)

Since the line passing through F is parallel to the y-axis, the points H, E, and F all share the same x-coordinate, x=α=2cosθ.
Since H lies on the x-axis, its coordinates are:
H(2cosθ,0)

The point E lies on the ellipse and has the x-coordinate x=2cosθ. In the first quadrant, its y-coordinate is:
y=bsinθ=3sinθ
Thus, the coordinates of E are:
E(2cosθ,3sinθ)

The equation of the tangent to the ellipse at point E(x1,y1) is:
xx14+yy13=1
Substituting x1=2cosθ and y1=3sinθ, we get:
x(2cosθ)4+y(3sinθ)3=1
Simplifying:
xcosθ2+ysinθ3=1

The tangent intersects the positive x-axis at point G. Setting y=0, we find:
x=2cosθ
So, the coordinates of G are:
G2cosθ0

Now, let us calculate the area of ΔFGH. The vertices are:
F(2cosθ,2sinθ), G2cosθ0, and H(2cosθ,0).

Since the x-coordinates of F and H are the same, the line segment FH is vertical (parallel to the y-axis).
The length of the base FH is:
Base=yF-yH=2sinθ

The height of the triangle is the horizontal distance from G to the vertical line x=2cosθ:
Height=xG-xH=2cosθ-2cosθ=21-cos2θcosθ=2sin2θcosθ

The area of ΔFGH is:
Area=12×Base×Height=12×(2sinθ)×2sin2θcosθ=2sin3θcosθ=2sin2θtanθ

Now, let us calculate the area for each given value of θ:

Case (I): θ=π4
Area=2sin2π4tanπ4=2×122×1=2×12×1=1
Therefore, (I) → (Q).

Case (II): θ=π3
Area=2sin2π3tanπ3=2×322×3=2×34×3=332
Therefore, (II) → (T).

Case (III): θ=π6
Area=2sin2π6tanπ6=2×122×13=2×14×13=123
Therefore, (III) → (S).

Case (IV): θ=π12
We know that:
sin2π12=1-cosπ62=1-322=2-34
And:
tanπ12=2-3
Substituting these values into the area formula:
Area=2×2-34×(2-3)=(2-3)22
Since (3-1)2=3-23+1=4-23=2(2-3), we have:
2-3=(3-1)22
Therefore:
Area=12(3-1)222=(3-1)48
Therefore, (IV) → (P).

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