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JEE Main 202229 JulyMorning Shift
Exam
JEE Main
Year
2022
Date
29 July
Shift
Morning Shift
Subject
Mathematics
Chapter
Circle

JEE Main 2022 · 29 July · Morning Shift · Mathematics · Circle

Let a line L pass through the point of intersection of the lines bx...

Let a line LL pass through the point of intersection of the lines bx+10y−8=0andbx + 10y - 8 = 0 and2x - 3y = 0,,b \in R - \left\{\dfrac{4}{3}\right\}.Iftheline. If the lineLalsopassesthroughthepoint(1,1)also passes through the point \left(1, 1\right) and touches the circle 17(x2+y2)=1617\left({x}^{2} + {y}^{2}\right) = 16, then the eccentricity of the ellipse x25+y2b2=1\dfrac{{x}^{2}}{5} + \dfrac{{y}^{2}}{{b}^{2}} = 1 is

Options

  1. A25\dfrac{2}{\sqrt{5}}
  2. B35\sqrt{\dfrac{3}{5}}
  3. C15\dfrac{1}{\sqrt{5}}
  4. D25\sqrt{\dfrac{2}{5}}

Correct answer

B. 35\sqrt{\dfrac{3}{5}}

Step-by-step solution

Line is passing through intersection of bx+10y−8=0and2x−3y=0bx + 10y - 8 = 0 and 2x - 3y = 0,

So its equation is given by,

\left(bx + 10y - 8\right) + \lambda\left(2x - 3y\right) = 0 . . . . . . . . . . \left(1\right)

Andthetheline is passing through \left(1, 1\right) soλ=b+2\lambda = b + 2

Now putting the value of λin\lambda inequation \left(1\right) we get,

⇒(3b+4)⇒ \left(3b + 4\right)x - (3b−4)\left(3b - 4\right)y - 8 = 0</p><p>Nowline(3b+4)x−(3b−4)y−8=0</p><p>Now line \left(3b + 4\right)x - \left(3b - 4\right)y - 8 = 0 is tangent to circle 17(x2+y2)=1617 \left({x}^{2} + {y}^{2}\right) = 16

So 8(3b+4)2+(3b−4)2=417\dfrac{8}{\sqrt{{\left(3b + 4\right)}^{2} + {\left(3b - 4\right)}^{2}}} = \dfrac{4}{\sqrt{17}}

⇒b2=2⇒ {b}^{2} = 2

Now eccentricity of the ellipse x25+y2b2=1\dfrac{{x}^{2}}{5} + \dfrac{{y}^{2}}{{b}^{2}} = 1 will be,

e2=1−b2a2{e}^{2} = 1 - \dfrac{{b}^{2}}{{a}^{2}}

⇒e=1−25=35⇒ e = \sqrt{1 - \dfrac{2}{5}} = \sqrt{\dfrac{3}{5}}

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