Join WhatsApp Icon JEE WhatsApp Group
Question 64

Let a tangent to the curve $$y^2 = 24x$$ meet the curve $$xy = 2$$ at the points $$A$$ and $$B$$. Then the mid-points of such line segments $$AB$$ lie on a parabola with the

The parabola $$y^2 = 24x$$ has $$4a = 24$$, so $$a = 6$$. A parametric point is $$(6t^2, 12t)$$ and the tangent at this point is $$ty = x + 6t^2$$.

This tangent meets the rectangular hyperbola $$xy = 2$$. Substituting $$x = ty - 6t^2$$:

$$(ty - 6t^2)y = 2 \Rightarrow ty^2 - 6t^2 y - 2 = 0$$

Let the y-coordinates of points A and B be $$y_1, y_2$$. By Vieta's formulas:

$$y_1 + y_2 = 6t, \quad y_1 y_2 = \frac{-2}{t}$$

The midpoint coordinates are:

$$k = \frac{y_1 + y_2}{2} = 3t \Rightarrow t = \frac{k}{3}$$

$$h = \frac{x_1 + x_2}{2} = \frac{1}{2}\left(\frac{2}{y_1} + \frac{2}{y_2}\right) = \frac{y_1 + y_2}{y_1 y_2} = \frac{6t}{-2/t} = -3t^2$$

Substituting $$t = k/3$$: $$h = -3 \cdot \frac{k^2}{9} = -\frac{k^2}{3}$$

The locus is $$y^2 = -3x$$, a parabola of the form $$y^2 = -4bx$$ with $$4b = 3$$, so $$b = \frac{3}{4}$$.

The directrix of $$y^2 = -3x$$ is $$x = \frac{3}{4}$$, i.e., $$4x = 3$$.

The length of the latus rectum is $$4b = 3$$.

The answer is Option A: directrix $$4x = 3$$.

Get AI Help

JEE Quant Questions | JEE Quantitative Ability

JEE DILR Questions | LRDI Questions For JEE

JEE Verbal Ability Questions | VARC Questions For JEE

Free JEE Topicwise Questions

JEE Rotational MotionJEE Units & MeasurementsJEE Atomic StructureJEE GravitationJEE Periodic Table & PeriodicityJEE StatisticsJEE Inverse Trigonometric FunctionsJEE Magnetism & Magnetic MaterialsJEE Sequences & SeriesJEE MatricesJEE Alternating CurrentsJEE Carboxylic AcidsJEE Permutations & CombinationsJEE Work, Energy & PowerJEE Electromagnetic InductionJEE Electronic DevicesJEE d and f-Block ElementsJEE Chemical KineticsJEE Heat TransferJEE Three Dimensional GeometryJEE Magnetic Effects of CurrentJEE Hydrocarbons - AromaticJEE Electromagnetic WavesJEE Aldehydes & KetonesJEE Hydrocarbons - AlkanesJEE Applications of DerivativesJEE EquilibriumJEE Indefinite IntegrationJEE Chemical ThermodynamicsJEE ElectrochemistryJEE ProbabilityJEE BiomoleculesJEE Continuity & DifferentiabilityJEE Kinetic Theory of GasesJEE Vector AlgebraJEE Hydrocarbons - AlkynesJEE Differential EquationsJEE Current & ResistanceJEE Straight LinesJEE WavesJEE Redox ReactionsJEE Hydrocarbons - AlkenesJEE DeterminantsJEE SolutionsJEE Ray OpticsJEE Dual Nature of Matter & RadiationJEE Chemical Bonding & Molecular StructureJEE Complex NumbersJEE Sets, Relations & FunctionsJEE Electric Charges & FieldsJEE Laws of MotionJEE Fluid MechanicsJEE Basic Concepts in ChemistryJEE Trigonometric FunctionsJEE LimitsJEE Laws of ThermodynamicsJEE Kinematics - 2D MotionJEE p-Block Elements (Groups 13-18)JEE Simple Harmonic MotionJEE Electric Potential & CapacitanceJEE Coordination CompoundsJEE JEE 2D GeometryJEE CirclesJEE Definite IntegrationJEE EMF & Circuit AnalysisJEE Surface TensionJEE Atoms & NucleiJEE Laboratory Experiments - XIJEE Number SystemJEE Basic Principles of Organic ChemistryJEE Wave OpticsJEE Quadratic EquationsJEE Alcohols, Phenols & EthersJEE Organic Compounds with HalogensJEE DifferentiationJEE Conic SectionsJEE Nitrogen-Containing CompoundsJEE ElasticityJEE Practical Organic ChemistryJEE Kinematics - 1D MotionJEE Purification & CharacterisationJEE Binomial Theorem
Ask AI