Are General Solutions of Linear ODEs Always Equivalent?

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SUMMARY

The discussion centers on the equivalence of general solutions for linear ordinary differential equations (ODEs), specifically the second-order linear ODE represented as ay''(t) + by'(t) + cy(t) = 0. The solution y(t) = c_1 exp(x_1 t) + c_2 exp(x_2 t) is established as more general than y(t) = A exp(σ t) cos(ω t - φ) when x_1 and x_2 are complex conjugates. However, if x_1 and x_2 are unequal real numbers, the solutions are not equivalent unless a non-standard interpretation involving complex constants for ω and φ is applied.

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Jhenrique
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Given the following ODE:

##ay''(t) + by'(t) + cy(t) = 0##

The following solution:

##y(t) = c_1 \exp(x_1 t) + c_2 \exp(x_2 t)##

is more general than:

##y(t) = A \exp(\sigma t) \cos(\omega t - \varphi)##

? Why?
 
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The solutions are equivalent if ##x_1## and ##x_2## are complex conjugate numbers.

They are not equivalent if ##x_1## and ##x_2## are unequal real numbers, unless you want to use a crazy interpretation of ##cos(\omega t - \varphi)## where ##\omega## and ##\varphi## are complex constants.
 

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