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Nov 2020 p31 q8
2273
The coordinates (x, y) of a general point of a curve satisfy the differential equation \(x \frac{dy}{dx} = (1 - 2x^2)y\), for \(x > 0\). It is given that \(y = 1\) when \(x = 1\).
Solve the differential equation, obtaining an expression for \(y\) in terms of \(x\).
Solution
Start by separating the variables:
\(\frac{1}{y} dy = \frac{1 - 2x^2}{x} dx\)
Integrate both sides:
\(\int \frac{1}{y} dy = \int \frac{1 - 2x^2}{x} dx\)
This gives:
\(\ln y = \ln x - x^2 + C\)
Use the initial condition \(y = 1\) when \(x = 1\) to find \(C\):