Solve: x''(t) = g(1 + c*x(t)) by method of variation of parameters

patbuzzatto

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Jul 1, 2017
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Hi, I have the exercise in the image that I need to resolve by method of variation of parameters:



7.1 A particle of unit mass moves in a straight line according to the following differential equation:

. . .\(\displaystyle \dfrac{d^2 x}{dt^2}\, =\, g(1\, +\, \epsilon x)\)

...where g and \(\displaystyle \epsilon\) are constants and \(\displaystyle 0\, <\, \epsilon x\, \ll\, 1.\) Use the method of the variation of parameters to show that the particle's motion is given approximately by:

. . .\(\displaystyle x\, =\, at\, +\, b\, +\, \frac{1}{2}gt^2\big[1\, +\, \epsilon \left(\frac{1}{12}gt^2\, +\, \frac{1}{3}at\, +\, b\right)\big]\)

...where a and b are the values of \(\displaystyle \frac{dx}{dt}\) and x at t = 0.




unfortunately I can't understand how it works for this equation, could someone help me?
exercicio_silvia.jpg
 
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