Join WhatsApp Icon JEE WhatsApp Group
Question 75

Let the solution curve $$y = y(x)$$ of the differential equation, $$\left[\frac{x}{\sqrt{x^2-y^2}} + e^{y/x}\right]x\frac{dy}{dx} = x + \left[\frac{x}{\sqrt{x^2-y^2}} + e^{y/x}\right]y$$ pass through the points $$(1, 0)$$ and $$(2\alpha, \alpha), \alpha > 0$$. Then $$\alpha$$ is equal to

The differential equation is:

$$\left[\frac{x}{\sqrt{x^2-y^2}} + e^{y/x}\right]x\frac{dy}{dx} = x + \left[\frac{x}{\sqrt{x^2-y^2}} + e^{y/x}\right]y$$

Let $$g(x,y) = \frac{x}{\sqrt{x^2-y^2}} + e^{y/x}$$. The equation becomes:

$$g \cdot x \frac{dy}{dx} = x + g \cdot y$$

$$g\left(x\frac{dy}{dx} - y\right) = x$$

Substituting $$y = vx$$ so $$\frac{dy}{dx} = v + x\frac{dv}{dx}$$:

$$x\frac{dy}{dx} - y = x\left(v + x\frac{dv}{dx}\right) - vx = x^2 \frac{dv}{dx}$$

Also, $$g = \frac{x}{\sqrt{x^2 - v^2x^2}} + e^v = \frac{1}{\sqrt{1-v^2}} + e^v$$.

So: $$\left(\frac{1}{\sqrt{1-v^2}} + e^v\right) x^2 \frac{dv}{dx} = x$$

$$\left(\frac{1}{\sqrt{1-v^2}} + e^v\right) dv = \frac{dx}{x}$$

Integrating both sides:

$$\int \frac{dv}{\sqrt{1-v^2}} + \int e^v \, dv = \int \frac{dx}{x}$$

$$\sin^{-1}(v) + e^v = \ln|x| + C$$

$$\sin^{-1}\left(\frac{y}{x}\right) + e^{y/x} = \ln|x| + C$$

Using the initial condition $$(1, 0)$$:

$$\sin^{-1}(0) + e^0 = \ln 1 + C \implies 0 + 1 = 0 + C \implies C = 1$$

So the solution is: $$\sin^{-1}\left(\frac{y}{x}\right) + e^{y/x} = \ln x + 1$$

Now substituting the point $$(2\alpha, \alpha)$$ where $$\alpha > 0$$:

$$\sin^{-1}\left(\frac{1}{2}\right) + e^{1/2} = \ln(2\alpha) + 1$$

$$\frac{\pi}{6} + \sqrt{e} = \ln(2\alpha) + 1$$

$$\ln(2\alpha) = \frac{\pi}{6} + \sqrt{e} - 1$$

$$2\alpha = \exp\left(\frac{\pi}{6} + \sqrt{e} - 1\right)$$

$$\alpha = \frac{1}{2}\exp\left(\frac{\pi}{6} + \sqrt{e} - 1\right)$$

Hence the correct answer is Option A: $$\dfrac{1}{2}\exp\left(\dfrac{\pi}{6} + \sqrt{e} - 1\right)$$.

Get AI Help

Create a FREE account and get:

  • Free JEE Mains Previous Papers PDF
  • Take JEE Mains paper tests

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