Is the Commutator of x and f(x) Always Zero?

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SUMMARY

The commutator of the position operator \( x \) and any function \( f(x) \) is always zero, as established through the application of Taylor's theorem. This theorem allows \( f(x) \) to be expressed as a polynomial, leading to the conclusion that the commutator \([f(x), x]\) can be expanded into terms of \([x^n, x]\), all of which evaluate to zero. Therefore, \( f(x) \) and \( x \) commute under the condition that both share the same domain, confirming the invariance of the domain of \( x \).

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Homework Statement


Is the commutator of x and any function of x zero?


Homework Equations


Taylor's theorem allows such a function to be expanded into polynomials, so that [f(x),x] may be expanded into terms of [x^n,x], which are all zero. Hence, f(x) and x commute.

The Attempt at a Solution



Is this a valid demonstration?
 
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You don't need a Taylor expansion. What do you think is x(f(x) - f(x)x?
 
This is true iff X and f(X) have the same domain, i.e. the domain of X is invariant.
 

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