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JEE Advanced 2018Paper 1
Exam
JEE Advanced
Year
2018
Paper
Paper 1
Subject
Mathematics
Chapter
Circle

JEE Advanced 2018 · Paper 1 · Mathematics · Circle

Paragraph: Let S be the circle in the xy – plane defined by the...

Paragraph: Let SS be the circle in the xyxy – plane defined by the equation x2+y2=4.{x}^{2} + {y}^{2} = 4 .

Question : Let E1E2{E}_{1}{E}_{2} and F1F2{F}_{1}{F}_{2} be the chords of SS passing through the point P0(1,1){P}_{0} ( 1,1 ) and parallel to the xx – axis and the yy – axis, respectively. Let G1G2{G}_{1}{G}_{2} be the chord of SS passing through P0{P}_{0} and having slope −1.- 1 . Let the tangents to SS at E1{E}_{1} and E2{E}_{2} meet at E3{E}_{3}, the tangents to SS at F1{F}_{1} and F2{F}_{2} meet at F3,{F}_{3}, and the tangents to SS at G1{G}_{1} and G2{G}_{2} meet at G3{G}_{3}. Then, the points E3,F3,{E}_{3}, {F}_{3}, and G3{G}_{3} lie on the curveParagraph: Let S be the circle in the xy – plane defined by the equation x ^ 2 + y ^ 2 = 4 . Question : Let E _ 1 E _ 2

Options

  1. Ax+y=4x + y = 4
  2. B(x−4)2+(y−4)2=16{\left(x - 4\right)}^{2} + {\left(y - 4\right)}^{2} = 16
  3. C(x−4)(y−4)=4\left(x - 4\right)\left(y - 4\right) = 4
  4. Dxy=4xy = 4

Correct answer

A. x+y=4x + y = 4

Step-by-step solution

Paragraph: Let S be the circle in the xy – plane defined by the equation x ^ 2 + y ^ 2 = 4 . Question : Let E _ 1 E _ 2 Co - ordinates of E1andE2{E}_{1}and{E}_{2} are obtained by solving y=1andx2+y2=4∴E1y = 1and{x}^{2} + {y}^{2} = 4 ∴ {E}_{1}\left(- \sqrt{3}, 1\right)andE2and{E}_{2}\left(\sqrt{3}, 1\right)Co−ordinatesofCo - ordinates of{F}_{1}and{F}_{2}areobtainedbysolvingare obtained by solvingx = 1and{x}^{2} + {y}^{2} = 4 {F}_{1}\left(1, \sqrt{3}\right)and{F}_{2}\left(1, - \sqrt{3}\right) Tangent at E1:−3x+y=4{E}_{1}: - \sqrt{3}x + y = 4 Tangent at E2:−3x+y=4∴E3(0,4){E}_{2}: - \sqrt{3}x + y = 4 ∴ {E}_{3}\left(0, 4\right) Tangent at F1:x+3y=4{F}_{1}: x + \sqrt{3}y = 4 Tangent at F2:x−3y=4∴F3{F}_{2}: x - \sqrt{3}y = 4 ∴ {F}_{3}\left(4, 0\right)AndsimilarlyG3And similarly{G}_{3}\left(2, 2\right) (0,4)\left(0, 4\right), \left(4, 0\right)andand\left(2, 2\right)liesonx+y=4liesonx + y = 4 Alternate solution 2: The required curve will be the polar of the pole P0(1,1){P}_{0} ( 1, 1 )w.rt. the circle S Hence its equation is T=0⇒x.1+y.1=4⇒x+y=4T = 0 ⇒ x.1 + y.1 = 4 ⇒ x + y = 4 Alternate solution 3: Let Q(h,k)Q( h, k ) is a general point on the curve containing points E3,F3{E}_{3} , {F}_{3}\text{and } {G}_{3} and a pair of tangents are drawn to the circle S from Q then the equation of the chord of contact will be T=xh+yk−4=0T = xh + yk - 4 = 0 since the chord of contact passes through P0(1,1){P}_{0} ( 1, 1 ) hence 1.h+1.k−4=0⇒1.h + 1.k - 4 = 0 ⇒ The point Q(h,k)Q( h, k ) lies on the line 1.x + 1.y - 4 = 0 ⇒ x + y - 4 = 0
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