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Which of the following differential equations has the solution y=3x^2?(a) \(\frac{d^2 y}{dx^2}\)-6x=0(b) \(\frac{dy}{dx}\)-3x=0(c) x \(\frac{d^2 y}{dx^2}\)–\(\frac{dy}{dx}\)=0(d) \(\frac{d^2 y}{dx^2}-\frac{3dy}{dx}\)=0This question was addressed to me in an international level competition.I want to ask this question from General and Particular Solutions of Differential Equation in chapter Differential Equations of Mathematics – Class 12

Answer»

Right answer is (c) X \(\frac{d^2 y}{dx^2}\)–\(\frac{dy}{dx}\)=0

The EXPLANATION is: Consider the function y=3x^2

Differentiating w.r.t x, we get

\(\frac{dy}{dx}\)=6x –(1)

Differentiating (1) w.r.t x, we get

\(\frac{d^2 y}{dx^2}\)=6

∴\(\frac{xd^2 y}{dx^2}-\frac{6dy}{dx}\)=6x-6x=0

Hence, the function y=3x^2 is a solution for the differential EQUATION x \(\frac{d^2 y}{dx^2}\)-6 \(\frac{dy}{dx}\)=0.



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