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JEE Main 20241 FebruaryMorning Shift
Exam
JEE Main
Year
2024
Date
1 February
Shift
Morning Shift
Subject
Mathematics
Chapter
Circle

JEE Main 2024 · 1 February · Morning Shift · Mathematics · Circle

Let C: x ^ 2 + y ^ 2 = 4 and C ^ ' : x ^ 2 + y ^ 2 - 4 + 9 = 0 be...

Let C: {x}^{2} + {y}^{2} = 4 and C′:x2+y2−4\lambdax+9=0{C}^{'}: {x}^{2} + {y}^{2} - 4\lambdax + 9 = 0 be two circles. If the set of all values of λ\lambda so that the circles CandC′C and C ' intersect at two distinct points, is R−[a,b],thenR - \left[a, b\right], then the point (8a+12,16b−20)liesonthecurve:point \left(8a + 12, 16b - 20\right) lies on the curve:

Options

  1. Ax2+2y2−5x+6y=3{x}^{2} + 2{y}^{2} - 5x + 6y = 3
  2. B5x2−y=−115{x}^{2} - y = - 11
  3. Cx2−4y2=7{x}^{2} - 4{y}^{2} = 7
  4. D6x2+y2=426{x}^{2} + {y}^{2} = 42

Correct answer

D. 6x2+y2=426{x}^{2} + {y}^{2} = 42

Step-by-step solution

Given: x2+y2=4{x}^{2} + {y}^{2} = 4

So, centre and radius of CC are \left(0, 0\right)\text{and}{r}_{1} = 2respectively.</p><p>Also,respectively.</p><p>Also,{C}^{'}: {x}^{2} + {y}^{2} - 4\lambdax + 9 = 0</p><p>So,centreandradiusof</p><p>So, centre and radius of{C}^{'} are \left(2\lambda, 0\right)andand{r}_{2} = \sqrt{4{\lambda}^{2} - 9}respectively.</p><p>respectively.</p><p>⇒ \left|{r}_{1} - {r}_{2}\right|<CC′<∣r1+r2∣< C{C}^{'} < \left|{r}_{1} + {r}_{2}\right|

⇒∣2−4λ2−9∣<∣2λ∣<2+4λ2−9⇒ \left|2 - \sqrt{4{\lambda}^{2} - 9}\right| < \left|2\lambda\right| < 2 + \sqrt{4{\lambda}^{2} - 9}

⇒4+4λ2−9−44λ2−9<4λ2⇒ 4 + 4{\lambda}^{2} - 9 - 4\sqrt{4{\lambda}^{2} - 9} < 4{\lambda}^{2}

⇒λ∈R...(i)</p><p>Also,⇒ \lambda \in R . . . \left(i\right)</p><p>Also,4{\lambda}^{2} < 4 + 4{\lambda}^{2} - 9 + 4\sqrt{4{\lambda}^{2} - 9}</p><p></p><p>⇒ 5 < 4\sqrt{4{\lambda}^{2} - 9}\left\{{\lambda}^{2} \ge \dfrac{9}{4}⇒λ∈(−∞,−32]⇒ \lambda \in \left(- \infty, - \dfrac{3}{2}\right] \cup \left[\dfrac{3}{2},\infty\right)</p><p>⇒ \dfrac{25}{16} < 4{\lambda}^{2} - 9</p><p></p><p>⇒ \dfrac{169}{64} < {\lambda}^{2}</p><p></p><p>⇒ \dfrac{169}{64} < {\lambda}^{2}</p><p></p><p>⇒ \lambda \in \left(- \infty, - \dfrac{13}{8}\right)∪(138,∞)\cup \left(\dfrac{13}{8}, \infty\right) . . . \left(ii\right)</p><p>Using(i)and(ii)</p><p>Using \left(i\right)\text{and}\left(ii\right),

⇒λ∈(−∞,−138)⇒ \lambda \in \left(- \infty, - \dfrac{13}{8}\right) \cup \left(\dfrac{13}{8}, \infty\right)</p><p></p><p>⇒ \lambda \in R - \left[−-\dfrac{13}{8}, \dfrac{13}{8}\right]

As per question a=a =- \dfrac{13}{8}andandb =\dfrac{13}{8}

∴∴ required point is \left(8a + 12, 16b - 20\right)≡(−1,6)≡ \left(- 1, 6\right) with satisfies option (d)( d ).

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