How to determine if x(t) is a solution to a system x'(t)=f(x)

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SUMMARY

The discussion centers on determining whether the function x(t) = sin(t) is a solution to the differential equation system x'(t) = f(x). It is established that x(t) = sin(t) does not satisfy the criteria for being a solution due to its explicit dependence on the variable t rather than solely on x. The derivative x'(t) = cos(t) does not conform to the form required for f(x), which necessitates a function of x alone. This highlights the importance of understanding the relationship between independent and dependent variables in differential equations.

PREREQUISITES
  • Understanding of differential equations
  • Knowledge of functions and their derivatives
  • Familiarity with the concept of solution sets in mathematical systems
  • Basic trigonometric functions and their properties
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  • Study the properties of solutions to ordinary differential equations (ODEs)
  • Learn about the existence and uniqueness theorems for ODEs
  • Explore the role of initial conditions in determining solutions
  • Investigate the implications of variable dependence in differential equations
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Mathematics students, educators, and anyone involved in solving or teaching differential equations will benefit from this discussion.

NicolaiTheDane
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For example having looked a solution sheet, I know that ##x(t)=\sin(t)## is not a solution for any system of the form ##\dot{x}(t)=f(x)##. I assume this is rather simple, but I simply cannot get my head around why it wouldn't be. I'm guessing it has to do with the dependence on ##x## rather then ##t## but I haven't gotten anywhere.
 
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If ##x(t) = \sin(t)##, then ##x'(t) = \cos(t) = \pm \sqrt{1- \sin^2(t)} = \pm \sqrt{1 - x(t)^2}##
 
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