Write the differential equation in the form x(y/y) = ln x + ln y and let u
Question:
Write the differential equation in the form x(y′/y) = ln x + ln y and let u = ln y.
Then
du/dx = y′/y and the differential equation becomes x(du/dx) = ln x + u or du/dx − u/x = (ln x)/x, which is first-order and linear. An integrating factor is e−∫ dx/x = 1/x, so that (using integration by parts)
d/dx [1/x u] = ln x/x2 and u/x = −1/x – (ln x/x) + c.
The solution is
ln y = −1 − ln x + cx or y = ecx−1/x.
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Related Book For
A First Course in Differential Equations with Modeling Applications
ISBN: 978-1305965720
11th edition
Authors: Dennis G. Zill
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