Find the equations of the trajectories?

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SUMMARY

The discussion centers on solving the differential equation y'' + y^3 = 0 to find the equations of the trajectories. The user derived the equation v²/2 + y⁴/4 = C, while the textbook states v² + y⁴/4 = C. The discrepancy raises questions about the application of the undamped case formula and the correctness of the algebraic manipulations performed. Participants suggest verifying the formula's applicability and checking for potential typographical errors in the textbook.

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Homework Statement


Find the equations of the trajectories of y"+y^3=0.

Homework Equations


None.

The Attempt at a Solution


The Undamped Case:
y"+p(y)=0
v(dv/dy)+p(y)=0
integrate
v^2/2+P(y)=C
---------------------------------
So following the formula above:
The answer I got is v^2/2+y^4/4=C, but the answer in the book says v^2+y^4/4=C. What's wrong?
 
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Did you, blindly, followed a formula?

What makes you think the formula applies in this case?
Did you follow the formula correctly?
Did you check your algebra?
Did you check your arithmetic?

Maybe the book made a typo?
 

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