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If a circle drawn by assuming a chord pa...

If a circle drawn by assuming a chord parallel to the transverse axis of hyperbola `(x^(2))/(a^(2))-(y^(2))/(b^(2))=1` as diameter always pases through (2, 0), then

A

`|a|=|b|=2`

B

`|b| ne |a|`

C

`|b|=|a|=1`

D

`|b|=|a|=3`

Text Solution

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The correct Answer is:
To solve the problem, we need to analyze the given hyperbola and the conditions for the circle drawn using a chord parallel to the transverse axis. Let's break down the solution step by step. ### Step 1: Understand the Hyperbola The equation of the hyperbola is given by: \[ \frac{x^2}{a^2} - \frac{y^2}{b^2} = 1 \] This hyperbola opens along the x-axis, and its transverse axis is horizontal. ### Step 2: Identify the Chord We need to consider a chord of the hyperbola that is parallel to the transverse axis. Let the endpoints of this chord be \( A(-a \sec \theta, b \tan \theta) \) and \( B(a \sec \theta, b \tan \theta) \). The y-coordinates of points A and B are the same, which is \( b \tan \theta \). ### Step 3: Equation of the Circle The circle with diameter AB can be expressed using the midpoint formula. The center of the circle is: \[ \left(0, b \tan \theta\right) \] The radius \( r \) of the circle is half the distance between points A and B, which is: \[ r = \frac{1}{2} \left| a \sec \theta - (-a \sec \theta) \right| = a \sec \theta \] The equation of the circle is: \[ \left(x - 0\right)^2 + \left(y - b \tan \theta\right)^2 = (a \sec \theta)^2 \] This simplifies to: \[ x^2 + \left(y - b \tan \theta\right)^2 = a^2 \sec^2 \theta \] ### Step 4: Condition for the Circle to Pass through (2, 0) For the circle to pass through the point (2, 0), we substitute \( x = 2 \) and \( y = 0 \) into the circle's equation: \[ 2^2 + \left(0 - b \tan \theta\right)^2 = a^2 \sec^2 \theta \] This simplifies to: \[ 4 + b^2 \tan^2 \theta = a^2 \sec^2 \theta \] ### Step 5: Use the Identity Using the identity \( \sec^2 \theta = 1 + \tan^2 \theta \), we can rewrite the equation: \[ 4 + b^2 \tan^2 \theta = a^2 (1 + \tan^2 \theta) \] Rearranging gives: \[ 4 = a^2 - b^2 \tan^2 \theta + a^2 \tan^2 \theta \] This can be factored as: \[ 4 = a^2 - (b^2 - a^2) \tan^2 \theta \] ### Step 6: Analyze the Conditions For the equation to hold for all values of \( \tan \theta \), the coefficient of \( \tan^2 \theta \) must be zero, leading to: \[ b^2 - a^2 = 0 \implies b^2 = a^2 \implies |b| = |a| \] Additionally, we also need to satisfy the condition when \( \tan^2 \theta \) is not involved, which gives: \[ a^2 = 4 \implies |a| = 2 \] ### Conclusion Thus, we conclude that: \[ |a| = |b| = 2 \]
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