Expected value (basic) (article) | Khan Academy
https://www.khanacademy.org/math/statistics-probability/random-variables-stats-library/random-variables-discrete/a/expected-value-basic
Web6 years ago. The expected value of a difference is the difference of the expected values, and the expected value of a non-random constant is that constant. Note that E (X), i.e. the theoretical mean of X, is a non-random constant. Therefore, if E (X) = µ, we have E (X − µ) = E (X) − E (µ) = µ − µ = 0.
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