Straight lines and conic sections: JEE Main-style questions
Original JEE Main-style questions on straight lines and conic sections, with a worked solution and the usual trap for each. Tap an option, or type a numerical answer, to check it.
Trap: Using \(|c_1 - c_2|\) before making the \(x\) and \(y\) coefficients equal gives \(22/13\).
Q2
·JEE Main style·Multiple choiceEllipse
The eccentricity of the ellipse \(\dfrac{x^2}{169} + \dfrac{y^2}{144} = 1\) is
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Answer: (c) \(\frac{5}{13}\)
\(a^2 = 169\), \(b^2 = 144\), and \(b^2 = a^2(1 - e^2)\): \(1 - e^2 = \dfrac{144}{169}\), so \(e^2 = \dfrac{25}{169}\) and \(e = \dfrac{5}{13}\).
Trap: \(25/169\) is \(e^2\): take the square root.
Q3
·JEE Main style·Numerical valueCircle and chord
Find the length of the chord that the \(x\)-axis cuts off on the circle \(x^2 + y^2 - 4x + 6y - 12 = 0\).
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Answer: 8
Put \(y = 0\): \(x^2 - 4x - 12 = 0\), so \((x - 6)(x + 2) = 0\) and \(x = 6\) or \(-2\).
Chord length \(= 6 - (-2) = 8\).
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