The variables x and y are related by the differential equation \((x^2 + 4) \frac{dy}{dx} = 6xy\).
It is given that \(y = 32\) when \(x = 0\). Find an expression for y in terms of x.
Solution
Start by separating the variables:
\(\frac{1}{y} \frac{dy}{dx} = \frac{6x}{x^2 + 4}\)
Integrate both sides:
\(\int \frac{1}{y} \, dy = \int \frac{6x}{x^2 + 4} \, dx\)
This gives:
\(\ln y = 3 \ln(x^2 + 4) + C\)
Use the initial condition \(y = 32\) when \(x = 0\):
\(\ln 32 = 3 \ln 4 + C\)
Solving for \(C\), we find:
\(C = \ln 32 - 3 \ln 4\)
Substitute back to find \(y\):
\(\ln y = 3 \ln(x^2 + 4) + \ln 32 - 3 \ln 4\)
\(\ln y = \ln((x^2 + 4)^3) + \ln \frac{32}{4^3}\)
\(\ln y = \ln((x^2 + 4)^3 \times \frac{1}{2})\)
\(y = \frac{1}{2}(x^2 + 4)\)
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