MCQMediumJEE 2025Circle Equation & Properties

JEE Mathematics 2025 Question with Solution

Let circle CC be the image of x2+y22x+4y4=0x^2 + y^2 - 2x + 4y - 4 = 0 in the line 2x3y+5=02x - 3y + 5 = 0 and AA be the point on CC such that OAOA is parallel to the x-axis and AA lies on the right-hand side of the centre OO of CC.

  • A

    33

  • B

    3+33 + \sqrt{3}

  • C

    434 - \sqrt{3}

  • D

    44

Answer

Correct answer:D

Step-by-step solution

Standard Method

Given: The circle x2+y22x+4y4=0x^2 + y^2 - 2x + 4y - 4 = 0 is reflected in the line 2x3y+5=02x - 3y + 5 = 0. Point AA lies on the reflected circle CC such that OAOA is parallel to the x-axis and AA is on the right-hand side of the centre OO of CC.

Find: The required value asked in the problem, as concluded from the provided solution.

First rewrite the given circle in standard form by completing the square:

(x1)2+(y+2)2=9(x-1)^2 + (y+2)^2 = 9

So the original circle has centre (1,2)(1,-2) and radius 33.

From the solution, the centre is then reflected across the line 2x3y+5=02x - 3y + 5 = 0, and the reflected circle is stated as

(x+3)2+(y4)2=9(x + 3)^2 + (y - 4)^2 = 9

Hence the reflected circle has centre O=(3,4)O = (-3,4) and radius 33.

Since OAOA is parallel to the x-axis and AA lies on the right-hand side of the centre, AA is the rightmost point of the reflected circle. Therefore its x-coordinate is centre x-coordinate plus radius:

xA=3+3=0x_A = -3 + 3 = 0

However, the provided the solution explicitly concludes with The Correct Option is D and the final answer 44.

So, the correct option is D.

Therefore, the required value is 44.

Note: The working shown in the solution is internally inconsistent with the stated geometry, but the solution explicitly marks option D as correct, so the extracted answer is D.

From the provided reflection steps

Given:

  • Original circle: x2+y22x+4y4=0x^2 + y^2 - 2x + 4y - 4 = 0
  • Reflection line: 2x3y+5=02x - 3y + 5 = 0

Find: The final value indicated by the provided solution.

The solution rewrites the circle as

(x1)2+(y+2)2=9(x-1)^2 + (y+2)^2 = 9

so the original centre is (1,2)(1,-2) and radius is 33.

In the second approach, the solution states that after reflection the new circle is

(x+3)2+(y4)2=9(x + 3)^2 + (y - 4)^2 = 9

which means the reflected centre is (3,4)(-3,4) and the radius remains 33.

The same the solution then gives the final statement: The correct option is 4\boxed{4}.

Therefore, the extracted answer is 44, i.e. option D.

Common mistakes

  • Finding the centre of the original circle incorrectly by not completing the square carefully. Here, x22xx^2 - 2x and y2+4yy^2 + 4y must be grouped properly; otherwise the reflected circle will be wrong. Complete the square first, then identify centre and radius.

  • Changing the radius after reflection. Reflection is an isometry, so the radius remains unchanged. Only the centre moves; the radius stays the same.

  • Misreading the condition OAOA is parallel to the x-axis. This means point AA lies horizontally from the centre OO, so for the right-hand side point you move one radius in the positive x-direction from the centre.

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