arthham

JEE Advanced 2016 · Conic Sections

The circle C1:x2+y2=3,C_{1} : x^{2} + y^{2} = 3, with centre at O, intersects the parabola x2=2yx^{2} = 2y at the point P in the first quadrant. Let the tangent to the circle C1C_{1} at P touch other two circles C2C_{2} and C3C_{3} at R2R_{2} and R3,R_{3}, respectively. Suppose C2C_{2} and C3C_{3} have equal radii 2⋅32\cdot \sqrt{3} and centres Q2Q_{2} and Q3,Q_{3}, respectively. If Q2Q_{2} and Q3Q_{3} lie on the y-axis, then (1)Q2Q3=12(2)R2R3=4⋅6(3)(1) Q_{2}Q_{3} = 12 (2) R_{2}R_{3} = 4\cdot \sqrt{6} (3) area of the triangle OR2R3_{2}R_{3} is 6⋅2(4)6\cdot \sqrt{2} (4) area of the triangle PQ2Q3_{2}Q_{3} is 4⋅24\cdot \sqrt{2}

Answers: A. Q2Q3=12Q_2Q_3 = 12 · B. R2R3=46R_2R_3 = 4\sqrt{6} · C. area of the triangle OR2R3OR_2R_3 is 626\sqrt{2}

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The circle C₁ : x² + y² = 3, with centre at O, intersects the parabola x² = 2y at the point P in the first quadrant. Let the tangent to the circle C₁, at P touches other two circles C₂ and C₃ at R₂ and R₃, respectively. Suppose C₂ and C₃ have equal radii 2√{3} and centres Q₂ and Q₃, respectively. If Q₂ and Q₃ lie on the y-axis, then C1:x2+y2=3 (centre O),parabola x2=2yC_1: x^2 + y^2 = 3 \ (\text{centre } O), \qquad \text{parabola } x^2 = 2y P=C1∩(x2=2y), in the first quadrantP = C_1 \cap (x^2 = 2y), \text{ in the first quadrant} C2,C3: radius 23, centres Q2,Q3 on the y-axisC_2, C_3: \text{ radius } 2\sqrt{3}, \ \text{centres } Q_2, Q_3 \text{ on the } y\text{-axis} Which of the statements (1)-(4) are correct?\text{Which of the statements (1)-(4) are correct?} 1. P=C1∩(x2=2y); tangent at P1.\ P = C_1 \cap (x^2 = 2y); \text{ tangent at } P 2. Qi=(0,q): distance from Qi to tangent=232.\ Q_i = (0, q): \text{ distance from } Q_i \text{ to tangent} = 2\sqrt{3} 3. find R2,R3, then test (1)-(4)3.\ \text{find } R_2, R_3, \text{ then test } (1)\text{-}(4) x2+(x22)2=3⇒x4+4x2−12=0x^2 + \left(\dfrac{x^2}{2}\right)^2 = 3 \Rightarrow x^4 + 4x^2 - 12 = 0 (x2+6)(x2−2)=0⇒x2=2⇒P(2,1)(x^2 + 6)(x^2 - 2) = 0 \Rightarrow x^2 = 2 \Rightarrow P(\sqrt{2}, 1) 2 x+y=3(tangent at P)\sqrt{2}\,x + y = 3 \qquad (\text{tangent at } P) Qi=(0,q): ∣q−3∣3=23⇒∣q−3∣=6Q_i = (0, q): \ \dfrac{|q - 3|}{\sqrt{3}} = 2\sqrt{3} \Rightarrow |q-3| = 6 q=9 or q=−3⇒Q2(0,9), Q3(0,−3)q = 9 \text{ or } q = -3 \Rightarrow Q_2(0,9), \ Q_3(0,-3) Ri=Qi−(qi−3)3(2,1)R_i = Q_i - \dfrac{(q_i - 3)}{3}(\sqrt{2}, 1) R2(−22,7),R3(22,−1)R_2(-2\sqrt{2}, 7), \qquad R_3(2\sqrt{2}, -1) Q2Q3=∣9−(−3)∣=12 ✓ (1) is correctQ_2Q_3 = |9 - (-3)| = 12 \ \text{✓ (1) is correct} R2R3=(42)2+(−8)2=96=46 ✓ (2) is correctR_2R_3 = \sqrt{(4\sqrt{2})^2 + (-8)^2} = \sqrt{96} = 4\sqrt{6} \ \text{✓ (2) is correct} [△OR2R3]=12∣(−22)(−1)−(7)(22)∣=62 ✓ (3) correct[\triangle OR_2R_3] = \dfrac{1}{2}\left|(-2\sqrt{2})(-1) - (7)(2\sqrt{2})\right| = 6\sqrt{2} \ \text{✓ (3) correct} [△PQ2Q3]=12⋅12⋅2=62≠42 ✗ (4) is false[\triangle PQ_2Q_3] = \dfrac{1}{2}\cdot 12 \cdot \sqrt{2} = 6\sqrt{2} \neq 4\sqrt{2} \ \text{✗ (4) is false} Correct statements: (1), (2), (3)\boxed{\text{Correct statements: (1), (2), (3)}}

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