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Axes are co-ordinate axes, A and B are e...

Axes are co-ordinate axes, A and B are ends of major axes and minor axis, area of `triangle`OAB is 16 sq units if e=`sqrt(3)/(2)` then equation of the ellipse is

A

`(x^(2))/(32)+y^2/8=1`

B

`(x^(2))/(64)+(y^(2))/(16)=1`

C

`(x^(2))/(64)+(y^(2))/(8)=1`

D

`(x^(2))/(64)+(y^(2))/(32)=1`

Text Solution

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The correct Answer is:
To solve the problem step by step, we will derive the equation of the ellipse given the area of triangle OAB and the eccentricity. ### Step 1: Understand the Geometry The points A and B are the ends of the major and minor axes of the ellipse, respectively. The origin O is the center of the ellipse. The area of triangle OAB can be calculated using the formula: \[ \text{Area} = \frac{1}{2} \times \text{base} \times \text{height} \] Here, the base is \(2A\) (the length of the major axis) and the height is \(2B\) (the length of the minor axis). ### Step 2: Set Up the Area Equation Given that the area of triangle OAB is 16 square units, we can write: \[ \frac{1}{2} \times 2A \times 2B = 16 \] This simplifies to: \[ 2AB = 16 \implies AB = 8 \] ### Step 3: Use the Eccentricity The eccentricity \(e\) is given as \(\frac{\sqrt{3}}{2}\). The relationship between the semi-major axis \(A\), semi-minor axis \(B\), and eccentricity \(e\) is: \[ e = \sqrt{1 - \frac{B^2}{A^2}} \] Substituting the value of \(e\): \[ \frac{\sqrt{3}}{2} = \sqrt{1 - \frac{B^2}{A^2}} \] ### Step 4: Square Both Sides Squaring both sides gives: \[ \left(\frac{\sqrt{3}}{2}\right)^2 = 1 - \frac{B^2}{A^2} \] This simplifies to: \[ \frac{3}{4} = 1 - \frac{B^2}{A^2} \] Rearranging gives: \[ \frac{B^2}{A^2} = 1 - \frac{3}{4} = \frac{1}{4} \] ### Step 5: Relate B to A From \(\frac{B^2}{A^2} = \frac{1}{4}\), we can express \(B\) in terms of \(A\): \[ B = \frac{A}{2} \] ### Step 6: Substitute into the Area Equation Now substitute \(B = \frac{A}{2}\) into the equation \(AB = 8\): \[ A \left(\frac{A}{2}\right) = 8 \] This simplifies to: \[ \frac{A^2}{2} = 8 \implies A^2 = 16 \implies A = 4 \] ### Step 7: Find B Using \(B = \frac{A}{2}\): \[ B = \frac{4}{2} = 2 \] ### Step 8: Write the Equation of the Ellipse The standard form of the ellipse is: \[ \frac{x^2}{A^2} + \frac{y^2}{B^2} = 1 \] Substituting \(A = 4\) and \(B = 2\): \[ \frac{x^2}{16} + \frac{y^2}{4} = 1 \] ### Final Answer The equation of the ellipse is: \[ \frac{x^2}{16} + \frac{y^2}{4} = 1 \]
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