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Circle question

2024 · 5 Apr · Shift 1 · Q37
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  5. /2024 · 5 Apr · Shift 1 · Q37

Circle question

2024 · 5 Apr · Shift 1 · Q37

JEE MainMathematicsCircleMCQ+4 / −1
Let a circle C of radius 1 and closer to the origin be such that the lines passing through the point (3,2)(3,2)(3,2) and parallel to the coordinate axes touch it. Then the shortest distance of the circle C from the point (5,5)(5,5)(5,5) is :
  1. A
    4 2\sqrt22​
  2. B
    4
  3. C
    5
  4. D
    2 2\sqrt22​
View written solutionFree

Correct answer: B

  1. Interpret the given condition

    The lines through (3,2)(3,2)(3,2) parallel to the coordinate axes are:

    • vertical line: x=3x=3x=3
    • horizontal line: y=2y=2y=2

    These two lines are tangent to the circle CCC of radius 111.

  2. Use the tangency condition to find the center

    Let the center of the circle be (h,k)(h,k)(h,k) and radius be 111.

    Since the line x=3x=3x=3 is tangent to the circle, the perpendicular distance from the center to this line must be 111: ∣h−3∣=1|h-3|=1∣h−3∣=1

    Since the line y=2y=2y=2 is tangent to the circle, the perpendicular distance from the center to this line must be 111: ∣k−2∣=1|k-2|=1∣k−2∣=1

    So, h=3±1 ⇒ h=2 or 4h=3\pm 1 \,\Rightarrow\, h=2 \text{ or } 4h=3±1⇒h=2 or 4 k=2±1 ⇒ k=1 or 3k=2\pm 1 \,\Rightarrow\, k=1 \text{ or } 3k=2±1⇒k=1 or 3

    Hence possible centers are: (2,1), (2,3), (4,1), (4,3)(2,1),\ (2,3),\ (4,1),\ (4,3)(2,1), (2,3), (4,1), (4,3)

  3. Use the condition “closer to the origin”

    Compute distance of each possible center from the origin:

    • For (2,1)(2,1)(2,1): 22+12=5\sqrt{2^2+1^2}=\sqrt522+12​=5​
    • For (2,3)(2,3)(2,3): 22+32=13\sqrt{2^2+3^2}=\sqrt{13}22+32​=13​
    • For (4,1)(4,1)(4,1): 42+12=17\sqrt{4^2+1^2}=\sqrt{17}42+12​=17​
    • For (4,3)(4,3)(4,3): 42+32=5\sqrt{4^2+3^2}=542+32​=5

    The circle closer to the origin has center (2,1)(2,1)(2,1).

  4. Find distance from (5,5)(5,5)(5,5) to the center

    Distance between (5,5)(5,5)(5,5) and center (2,1)(2,1)(2,1) is: d=(5−2)2+(5−1)2d=\sqrt{(5-2)^2+(5-1)^2}d=(5−2)2+(5−1)2​ d=32+42=25=5d=\sqrt{3^2+4^2}=\sqrt{25}=5d=32+42​=25​=5

  5. Find the shortest distance from the point to the circle

    Since the radius is 111, the shortest distance from the point to the circle is: d−r=5−1=4d-r=5-1=4d−r=5−1=4

  6. Check options

    • A: 424\sqrt242​ ❌
    • B: 444 ✅
    • C: 555 ❌
    • D: 222\sqrt222​ ❌

Therefore, the correct answer is B.

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