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GATE 2019 AE – Question 43

Engineering Mathematics · Differential Equations: First order linear ODEs and higher order linear ODEs with constant coefficients · 2 marks · Numerical answer

For $dy/dx=y^2$ with y(1)=−1, the source asks for y(−2). Give the value intended by the official key.

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Correct answer: 0.5 to 0.5

Explanation

Separation yields −1/y=x+C; y(1)=−1 gives C=0, hence the expression y=−1/x. Substituting −2 gives the officially intended value 0.5. There is a domain caveat: the initial-value solution through x=1 has maximal interval x>0 and cannot pass through the pole at x=0. Thus 0.5 is the value of the continued algebraic expression on the other interval, not a value on the same connected IVP solution.

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