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JEE Main 202325 JanuaryMorning Shift
Exam
JEE Main
Year
2023
Date
25 January
Shift
Morning Shift
Subject
Mathematics
Chapter
Circle

JEE Main 2023 · 25 January · Morning Shift · Mathematics · Circle

The points of intersection of the line ax + by = 0 , ( a ≠ b ) and...

The points of intersection of the line ax+by=0ax + by = 0, (a≠b)( a \ne b ) and the circle x2+y2−2x=0{x}^{2} + {y}^{2} - 2x = 0 are A(α,0)A ( \alpha, 0 ) and B(1,β)B ( 1, \beta ). The image of the circle with ABAB as a diameter in the line x+y+2=0x + y + 2 = 0 is :

Options

  1. Ax2+y2+5x+5y+12=0{x}^{2} + {y}^{2} + 5x + 5y + 12 = 0
  2. Bx2+y2+3x+5y+8=0{x}^{2} + {y}^{2} + 3x + 5y + 8 = 0
  3. Cx2+y2+3x+3y+4=0{x}^{2} + {y}^{2} + 3x + 3y + 4 = 0
  4. Dx2+y2−5x−5y+12=0{x}^{2} + {y}^{2} - 5x - 5y + 12 = 0

Correct answer

A. x2+y2+5x+5y+12=0{x}^{2} + {y}^{2} + 5x + 5y + 12 = 0

Step-by-step solution

Given,

The points of intersection of the line ax+by=0,(a≠b)ax + by = 0, ( a \ne b ) and the circle x2+y2−2x=0{x}^{2} + {y}^{2} - 2x = 0 are A(α,0)A\left(\alpha, 0\right) and B ( 1, \beta )then,</p><p>Forpointthen,</p><p>For pointA\left(\alpha, 0\right)</p><p></p><p>a ( \alpha ) + b ( 0 ) = 0 ⇒ \alpha = 0</p><p>And,</p><p>And,{\alpha}^{2} - 2\alpha = 0 ⇒ \alpha = 0, 2</p><p>Forpoint</p><p>For pointB ( 1, \beta )</p><p></p><p>a + b\beta = 0</p><p>Or,</p><p>Or,\beta = \dfrac{- b}{a}</p><p>And,</p><p>And,1 + {\beta}^{2} - 2 = 0</p><p></p><p>⇒ \beta = \pm 1</p><p></p><p>∵ a \ne btherefore,</p><p>Onlypossibilitytherefore,</p><p>Only possibility\alpha = 0, \beta = 1</p><p>Pointsare</p><p>Points areA\left(0, 0\right)andandB\left(1, 1\right)</p><p>SothecentreofthecirclewithdiameterABis(12,12)</p><p>So the centre of the circle with diameter AB is \left(\dfrac{1}{2}, \dfrac{1}{2}\right) and radius r=12r = \dfrac{1}{\sqrt{2}}

Now the image of \left(\dfrac{1}{2}, \dfrac{1}{2}\right)aboutthelineabout the linex + y + 2 = 0is,</p><p>is,</p><p>\dfrac{x - \dfrac{1}{2}}{1} = \dfrac{y - \dfrac{1}{2}}{1} = \dfrac{- 2\left(\dfrac{1}{2} + \dfrac{1}{2} + 2\right)}{{1}^{2} + {1}^{2}}</p><p></p><p>⇒ \dfrac{x - \dfrac{1}{2}}{1} = \dfrac{y - \dfrac{1}{2}}{1} = - 3</p><p></p><p>⇒Centreofimagecircleis(−52,−52)Centre of image circle is \left(- \dfrac{5}{2}, - \dfrac{5}{2}\right)

Equation of image circle

(x+52)2+(y+52)2=(12)2{\left(x + \dfrac{5}{2}\right)}^{2} + {\left(y + \dfrac{5}{2}\right)}^{2} = {\left(\dfrac{1}{\sqrt{2}}\right)}^{2}

⇒x2+y2+5x+5y+12=0⇒ {x}^{2} + {y}^{2} + 5x + 5y + 12 = 0

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