Question Details

Let T1 and T2 be two distinct common tangents to the ellipse E:x26+y23=1 and the parabola P:y2=12x. Suppose that the tangent T1 touches P and E at the points A1 and A2, respectively, and the tangent T2 touches P and E at the points A4 and A3, respectively. Then which of the following statements is/are true?

Options

A

The area of the quadrilateral A1A2A3A4 is 35 square units

B

The area of the quadrilateral A1A2A3A4 is 36 square units

C

The tangents T1 and T2 meet the x-axis at the point (-3, 0)

D

The tangents T1 and T2 meet the x-axis at the point (-6, 0)

Show Answer

Correct Answer :

Option A

The area of the quadrilateral A1A2A3A4 is 35 square units

Option C

The tangents T1 and T2 meet the x-axis at the point (-3, 0)

Solution :

The correct options are:
The area of the quadrilateral A1A2A3A4 is 35 square units
The tangents T1 and T2 meet the x-axis at the point (-3, 0)

Let us analyze the given curves step-by-step and find their common tangents and points of contact.

Step 1: Equation of Common Tangents

The equation of the given parabola is:

y2=12x

Here, 4a=12a=3.

Any tangent to the parabola y2=12x with slope m is given by:

y=mx+3m

Or in standard form:

mx-y+3m=0

The equation of the given ellipse is:

x26+y23=1

Here, a2=6 and b2=3.

For the line y=mx+3m to be tangent to the ellipse, the condition of tangency c2=a2m2+b2 must be satisfied:

3m2=6m2+3

9m2=6m2+3

Multiplying both sides by m2:

9=6m4+3m22m4+m2-3=0

Factoring the quadratic equation in m2:

(2m2+3)(m2-1)=0

Since m2 must be real and positive, we get m2=1m=±1.

Therefore, the two common tangents are:

For m=1: T1:y=x+3
For m=-1: T2:y=-x-3

Step 2: Intersection of Tangents with the x-axis

Setting y=0 in both tangent equations:

For T1: 0=x+3x=-3
For T2: 0=-x-3x=-3

Thus, both tangents T1 and T2 meet the x-axis at the point (-3, 0).

Step 3: Finding the Points of Contact

For a parabola y2=4ax, the point of contact for a tangent with slope m is am2,2am.

• For T1 (m=1), the point of contact on P is A1=312,2(3)1=(3,6).
• For T2 (m=-1), the point of contact on P is A4=3(-1)2,2(3)-1=(3,-6).

For an ellipse x2a2+y2b2=1, the point of contact for a tangent line y=mx+c is given by -a2mc,b2c.

• For T1 (m=1,c=3), the point of contact on E is A2=-6(1)3,33=(-2,1).
• For T2 (m=-1,c=-3), the point of contact on E is A3=-6(-1)-3,3-3=(-2,-1).

Step 4: Area of Quadrilateral A1A2A3A4

The four vertices are:

A1=(3,6), A2=(-2,1), A3=(-2,-1), A4=(3,-6)

Since the shape is an isosceles trapezium symmetric about the x-axis, we can calculate its area using the formula for the area of a trapezium:

Area=12×(sum of parallel sides)×(distance between parallel sides)

Parallel side 1 (A1A4): length = 6-(-6)=12
Parallel side 2 (A2A3): length = 1-(-1)=2
Distance between parallel sides (along x-axis): 3-(-2)=5

Substitute these values into the area formula:

Area=12×(12+2)×5=12×14×5=35 square units

Hence, the area of the quadrilateral A1A2A3A4 is 35 square units and the tangents meet the x-axis at (-3, 0).

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