Set up differential equations

Questions
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1

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I’d wonder if anyone can help me set up these differential equations. I don’t know how to experss an derivative of a function calculated at certain point in a differential equation in Mathematica.

Thanks.

2

Perhaps start with the documentaiton for DSolve

http://reference.wolfram.com/language/ref/DSolve.html

or NDSolve

http://reference.wolfram.com/language/ref/NDSolve.html